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'    REESE  LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 
Deceived        Jfoa^zh-          >  **9     •/  9OO 

No.  J  8  (o  %  *7    .   Clots  No. 


MODERN   PRACTICE 


ELECTRIC   TELEGRAPH 


MODERN    PRACTICE 


OF   THE 


ELECTRIC  TELEGRAPH 

A  TECHNICAL   HANDBOOK 

FOR 

ELECTRICIANS,  MANAGERS,  AND  OPERATORS 

WITH    185    ILLUSTRATIONS 
BY 

FRANKLIN    LEONARD    POPE 

PAST    PRESIDENT    OF    THB    AMERICAN    INSTITUTE    OF    ELECTRICAL    ENGINEERS;    MEMBER     OF 
THE     INSTITUTION    OF    ELECTRICAL    ENGINEERS    (LONDON) 


FIFTEENTH    EDITION  .REWRITTEN   AND    ENLARGED 


OF  THE 

UNIVERSITY 


NEW   YORK 
D.   VAN    NOSTRAND    COMPANY 

LONDON 

SAMPSON,   LOW,    MARSTON    &    CO. 
(LIMITED-) 

1899 


COPYRIGHT,  1891 
O.  VAN  NOSTRAND  COMPANY 


Braunworth,  Munn  &  Barber, 

Printers  and  Binders, 

Brooklyn,  N.  Y. 


IN  AFFECTIONATE  REMEMBRANCI 
OF  MY  FORMER  CHIEF 


ENGINEER   OF 

THE     AMERICAN     TELEGRAPH    COMPANY,     1861-1864 

UNDER   WHOSE 

ENLIGHTENED,  PROGRESSIVE,  AND  LIBERAL  ADMINISTRATION  THE 

METHODS  OF  MODERN  SCIENCE  WERE  FIRST  APPLIED  TO 

AMERICAN  TELEGRAPHY 


MORSE  (SAMUEL  FINLEY  BREESE),  Inventor  of  the  recording  electro-magnetic 
telegraph,  born  in  Charlestown,  Mass.,  April  27,  1791;  graduated  at  Yale,  1810; 
studied  art  in  the  Royal  Academy  of  London,  1811-15,  under  Benjamin  West.  In 
1829  he  again  visited  Europe  for  further  study  of  his  profession,  and  while  returning 
home  in  1832,  on  board  the  ship  Sully,  conceived  and  made  drawings  of  his  recording 
telegraph  (see  J.  D.  REID  :  The  Telegraph  in  America^  chapters  vi.,  vii.).  From 
this  time  until  his  death  he  was  unremittingly  employed  with  his  invention,  passing 
meantime  through  many  vicissitudes  of  fortune,  and  some  most  painful  experiences. 
He  was  first  professor  of  fine  arts  in  the  University  of  the  City  of  New  York,  in  one  of 
the  rooms  of  which  institution  he  set  up  in  1835  his  first  crude  recording  telegraphic  ap- 
paratus, now  preserved  in  the  cabinet  of  the  Western  Union  Company  in  New  York. 
In  1837,  Alfred  Vail,  a  skillful  mechanic  and  inventor,  became  his  partner  in  the  enter- 
prise. Vail  entirely  reconstructed  the  apparatus,  and  embodied  it  in  the  practical 
form  in  which  it  was  first  introduced  to  the  commercial  world.  After  a  series  of  dis- 
couragements that  would  have  utterly  disheartened  most  men,  Morse,  assisted  by  Vail, 
established  in  1844,  under  an  appropriation  from  Congress,  the  first  line  between 
Washington  and  Baltimore.  On  May  24  of  that  year,  Morse  put  to  the  test  the  great 
experiment  on  which  his  mind  had  been  laboring  for  many  anxious  and  weary  years. 
His  triumph  was  complete.  Honors  and  riches  were  showered  upon  him  at  home  and 
abroad.  Professor  Morse  was  a  man  of  great  simplicity  of  character,  firm  in  his 
friendships,  and  most  persistent  and  exhaustive  in  all  his  undertakings.  He  wielded 
the  pen  of  a  ready  writer,  and  his  genius,  learning,  and  taste  were  illustrated  by 
numerous  contributions  to  the  press,  evincing  not  only  graceful  rhetoric  but  elaborate 
and  well-sustained  argument.  On  June  10,  1871,  a  bronze  statue  of  Morse,  erected  by 
the  contributions  of  the  thousands  of  telegraphic  employees  in  America,  was  unveiled 
with  imposing  ceremonies  in  Central  Park,  New  York.  He  died  in  New  York, 
April  2,  1872. 


PREFACE. 


A, MOST  a  quarter  of  a  century  has  passed  since  the  publication 
of  the  first  edition  of  this  work.  During  that  period,  and 
more  especially  during  the  past  ten  years,  the  progress  which  has 
been  made  in  the  application  of  electricity  to  the  industrial  arts  has 
been  literally  unprecedented,  while  the  extraordinary  practical  results 
which  have  been  attained  have  exerted  a  reflex  action  in  stimulating 
in  an  equal  degree  the  advancement  of  electrical  science ;  an  ad- 
vancement which  has  not  been  without  its  influence  upon  the  theory 
and  practice  of  the  electric  telegraph.  This  circumstance  has  at 
length  rendered  necessary,  not  a  mere  revision  of  the  original  treatise, 
but  the  preparation,  in  fact,  of  an  entirely  new  work  throughout. 

To  the  intelligent  and  observant  mind  of  youth,  the  art  of  teleg- 
raphy possesses  a  singular  fascination,  and  in  many  instances  its 
pursuit  tends  to  excite  a  spirit  of  scientific  inquiry,  not  only  com- 
mendable in  itself,  but  valuable  as  establishing  a  sure  foundation  for 
future  success  in  broader  fields  of  labor.  It  has  been  the  aim  of 
the  author  to  supply  a  knowledge,  not  only  of  the  principles  and 
practice  of  telegraphy,  but  of  the  theory  of  electricity  and  the 
methods  of  electrical  measurement,  which  should  be  of  the  highest 
possible  value  to  every  person  entrusted  with  the  care  and  manage- 
ment of  telegraphic  apparatus.  It  has,  however,  been  deemed  advis- 
able to  somewhat  restrict  the  scope  of  the  work,  and  hence  the  auto- 
matic, type-printing,  synchronous,  submarine,  and  other  methods, 
requiring  on  the  part  of  the  practitioners  a  special  training  apart 
from  a  knowledge  of  the  ordinary  system,  have  been  excluded.  The 
construction  and  maintenance  of  aerial,  subterranean,  and  submarine 
lines  has  also,  by  a  natural  process  of  evolution  in  the  progress  of 


viii  .  Preface. 

the  art,  become  a  separate  profession,  and  the  subject  can  therefore 
receive  but  brief  notice  in  a  work  primarily  designed  for  the  guidance 
and  instruction  of  the  practical  operator. 

In  the  treatment  of  the  subject,  the  use  of  mathematics  has  been 
rendered  unnecessary  by  the  free  introduction  of  concrete  examples, 
illustrative  of  methods  and  processes  of  arithmetical  computation 
available  in  electrical  investigations.  From  the  many  methods  of 
electrical  measurement,  as  applied  to  the  solution  of  practical  prob- 
lems, a  selection  has  been  made,  embracing  only  those  which  have 
proved  to  be  most  directly  applicable  to  every-day  work. 

The  numerous  authorities  which  have  been  consulted  in  the  prepa- 
ration of  the  present  treatise  have  been  carefully  indicated  in  the 
foot-notes ;  in  many  instances  with  the  addition  of  the  titles  of  pub- 
lications which  may  profitably  be  consulted  by  the  student  desiring 
to  investigate  more  minutely  some  particular  branch  of  the  subject. 
These  references  are  intended  to  constitute,  in  some  sense,  a  key  to 
the  standard  literature  of  electricity,  although  from  the  nature  of  the 
case,  by  no  means  an  exhaustive  one. 

It  is  hoped  that  the  brief  biographical  notices  of  men  who  have 
distinguished  themselves  in  connection  with  electrical  science  will 
be  found  to  add  something  to  the  value  of  the  work,  especially  as 
the  facts  given  are  sometimes  difficult  of  access  to  the  ordinary 
reader. 

The  author  acknowledges  with  pleasure  his  indebtedness  to  many 
friends  for  courtesies  extended,  especially  to  Professor  Moses  G. 
Farmer  of  Eliot,  Me.,  and  Messrs.  E.  M.  Barton,  of  the  Western 
Electric  Company  of  Chicago,  E.  S.  Greeley  of  New  York,  and 
Edward  Weston,  of  Newark,  N.  J. 

EDGEWOOD  FARM,  ELIZABETH,  N.  J., 
September  z,  1891. 


CONTENTS. 


CHAPTER    I. 

INTRODUCTORY. 

FAD* 

Fundamental  Principles,  §§  i,  2,  3. — Nature  of  Electricity,  4. — Ele- 
ments of  Electric  Telegraph,  5 I 

CHAPTER     II. 

SOURCES   OF    ELECTRICITY. 

Origin  of  Electricity,  §§  6,  7. — Voltaic  Element,  8. — Description  of  the 
Typical  Cell,  9,  10. — Phenomena  of  Cell,  n,  12,  13. — Chemistry  of 
the  Voltaic  Effect,  14,  15. — Gravity  Cell,  16. — Specific  Gravity,  17. — 
Hydrometer,  18. — Charging  the  Cell,  19,  20,  21. — Copper  and  Zinc 
Solutions,  22. — Specific  Gravities  of  Battery  Solutions,  23. — Instal- 
lation of  Gravity  Cell,  24,  25. — Modified  Form  of  Copper  Plate,  26, 
27. —  Formation  of  Electric  Circuit,  28,  29,  30. — Nomenclature  of 
Electric  Circuit,  31. — Chemical  Reactions  arising  in  Closed  Cir- 
cuit, 32. — Effect  of  Continued  Action,  33,  34,  35. — Rate  of  Con- 
sumption of  Material,  36. — Maintenance  of  Cell,  37. — Prevention 
of  Evaporation,  38,  39. — Dismantling  Cell,  40. — Diffusion  of  Solu- 
tion within  Cell,  41,  42. — Neutralizing  Zinc  Solution,  43. — Waste 
Products  of  Cell,  44,  45. — Other  Forms  of  Cell,  46,  47. — Lockwood 
Cell,  48. — Daniell  Cell,  49,  50. — Maintenance  of  Daniell  Cell,  51. — 
Renewal  of  Daniell  Cell,  52. — Intermingling  of  Solutions,  53,  54. — 
Choice  of  Battery  Materials,  55,  56. — General  Directions  for  Care 
of  Cells,  57. — Oxide  of  Copper  Cell,  58. — Setting  Up  and  Maintain- 
ing Oxide  of  Copper  Cell,  59. — Chemical  Reactions  of  Oxide  of 
Copper  Cell,  60. — Grove  and  Bunsen  Cells,  61. — Wasteless  Battery 
Zinc,  6ia 3 

CHAPTER     III. 

SOURCES  OF   ELECTRICITY. — (Continued.} 

Magneto-Electricity,  §  62. — Magnetism,  63. — Magnetic  Needle,  64. — 
Phenomena  of  Magnetic  Induction,  65. — Polarity  of  Magnet,  66. — 
Horseshoe  Magnet  and  Armature,  67. — Magnetic  Spectrum,  68. — 
Magnetic  Field,  69. — Lines  of  Magnetic  Force,  70,  71. — Attraction 
and  Repulsion,  72. — Electric  Current  Produced  by  Magnetic  Field, 
73.  74- — Transformation  of  Mechanical  Power  into  Electricity  and 


x  Contents. 


PAGE 


Heat,  75. — Direction  of  Induced  Current,  76. — Mutual  Reactions 
of  Current  and  Magnet,  77. — Summary  of  Magneto-Electric  Phe- 
nomena, 78. — Dynamo-Electric  Machine,  79. — Theoretical  Dynamo, 
80,  81.— Frictional  Electricity,  82. — Thermo-Electricity,  83 24 

CHAPTER     IV. 

THEORY    OF    QUANTITATIVE    ELECTRICAL    MEASUREMENT. 

Electric  Current,  §  85. — Manifestations  of  Current,  86. — Importance  of 
Quantitative  Measurement,  87.  —  Fundamental  Units  of  Mass, 
Space,  and  Time,  88. — Illustration  of  Absolute  System  of  Measure- 
ment, 89. — Derivation  of  Electrical  and  Magnetic  Units,  90. — C.  G. 
S.  Units  of  Force  and  Work,  91. — Conservation  of  Force,  92. — 
Electric  Field  of  Force,  93. — Relation  of  Current  Force  to  Mechan- 
ical Force,  94. — Galvanoscope  and  Galvanometer,  95. — Tangent 
Galvanometer,  96.— Character  of  Electrical  Measurements,  97. — 
Characteristics  Capable  of  Measurement,  98. — Apparatus  for  Meas- 
urement, 99. — Ammeter,  Voltmeter,  and  Calorimeter,  100 35 

CHAPTER     V. 

THE   LAWS   AND   CONDITIONS    OF    ELECTRICAL    ACTION. 

Apparatus  Required  by  Student,  §  101. — Construction  of  Tangent  Gal- 
vanometer, 102,  103,  104,  105. — Construction  of  Rheostat,  106. — 
Preparation  for  Experiments,  107. — Effect  of  Varying  Number  of 
Cells  in  Series,  108.— Cells  in  Parallel  Series,  109. — Cells  in  Paral- 
lel, no. — Increasing  Length  of  Conducting  Circuit,  in,  112,  113. — 
Conditions  which  Determine  Quantity  of  Current,  114. — Resist- 
ance, 115. — Conductors  and  Insulators,  116,  117. — Specific  Resist- 
ance of  Different  Metals,  1170. — Conditions  Affecting  Resistance, 
118. — Provisional  Theory  of  Electricity,  119. — Mechanical  Ana- 
logue of  Electrical  Action,  120. — Conception  of  Potential  and 
Electromotive  Force,  121. — Practical  Electric  Units,  122. — Ampere, 
123.  —  Coulomb,  123^.  —  Volt,  124.  —  Ohm,  125.  —  Resistance  of 
Liquids,  126. — Ohm's  Law,  127. — Joule's  Law,  128,  129. — Experi- 
mental Proof  of  Ohm's  Law,  130. — Internal  Resistance  of  Cell, 
131. — First  Case,  132. — Second  Case,  133. — Law  of  Joint  Resist- 
ances, 134,  135. — Third  Case,  136,  137,  138,  139. — Branch  or  De- 
rived Circuits,  140. — Electric  Potential,  141,  142. — Illustration  of 
Fall  of  Potential,  143.— Fall  of  Potential  Proportionate  to  Resist- 
ance, 144. — Graphic  Illustration  of  Electric  Circuit,  145. — Fall  of 
Potential  in  Non-homogeneous  Circuit,  146. — Electrostatic  Capacity, 
147. — Farad,  148. — Power,  or  Rate  of  Work,  149. — Watt,  150. — 
Current  Induction,  151. — Electrical  Dimensions  of  Voltaic  Cell, 
152. — E.  M.  F.  and  Resistance  of  Cell,  153.— Quantity  and  Cost 
of  Materials  Consumed  in  Battery,  154,  155,  156. — Production 
of  Electricity  in  Proportion  to  Material  Consumed,  157. — Con- 


Contents.  xi 

FACE 

sumption  of  Material  in  Series  of  Cells,  158. — Electrical  Dimen- 
sions of  Edison-Lalande  Cell,  159. — Effect  of  Temperature  upon 
Resistance  of  Metallic  Conductors,  160,  161. — Effect  of  Tempera- 
ture upon  Resistance  of  Liquids,  162. — Effect  of  Temperature  upon 
Resistance  of  Daniell  Cell,  163,  164 45 


CHAPTER     VI. 

THE    LAWS    OF    ELECTRO-MAGNETISM. 

Elements  of  Electro-Magnet,  §§  166,  167. — Polarity  of  Electro-Magnet 
Determined  by  Direction  of  Current,  168. — Lines  of  Force  as  a 
Measure  of  Magnetic  Field,  169,  170. — Unit  of  Magnetism,  171. — 
Magneto-motive  Force,  172. — Effect  of  Iron  in  Helix,  173. — Effect 
of  Magnetization  upon  Soft  Iron,  174,  175. — Magnetic  Saturation, 
176. —  Magnetization  Proportional  to  Ampere-turns,  177. — The 
Magnetic  Circuit,  178. — Magnetic  Permeability,  179. — Law  of  Mag- 
netic Circuit,  180. — Determination  of  Magnetic  Reluctance,  181. — 
Ratio  of  Attractive  Force  to  Distance,  182. — Construction  of  Tele- 
graph Magnet,  183. — Theoretical  Proportions  of  Telegraph  Mag- 
net, 184. — Effect  of  Position  of  Windings,  185. — Helix  of  Coil, 
186. — Relation  of  Thickness  and  Length  of  Wire  to  Number  of 
Turns,  187. — Dimensions  and  Resistances  of  Magnet  Wires,  188. — 
Thickness  of  Spaces  between  Turns  of  Wire,  189.  —  American 
Standard  Wire  Gauge,  190.  —  British  Standard  Wire  Gauge,  191. — 
Instruments  for  Gauging  Wire,  192. — Adaptation  of  Magnets  to 
Working  Currents,  193,  194. — Spectrum  of  Electro-Magnet,  194. — 
Magnetic  Hysteresis,  195. — Induction  of  a  Current  upon  Itself,  196. 
— Magnet  Cores  must  not  be  Hardened,  197. — Effect  of  Self-induc- 
tion and  Hysteresis  in  Telegraph  Magnets,  198. — Other  Indirect 
Causes  of  Retardation  in  Electro-Magnets,  199. — Electro-Magnet  • 
with  Polarized  Armature,  200,  201. — Combinations  of  Permanent 
and  Electro-Magnets,  202 80 

CHAPTER     VII. 

TELEGRAPHIC     CIRCUITS. 

Telegraphic  Circuits,  §§  203,  204,  205. — Open  and  Closed  Circuits,  206. 
— Drawings  of  Electric  Apparatus,  207. — Conventional  Representa- 
tions of  Circuits  and  Apparatus,  208. — The  Earth  as  an  Electrical 
Conductor,  209. — Ground  Connection,  210. — Advantages  of  the 
Earth  Circuit,  211. — Open  Circuit,  212. — Closed  Circuit,  213. — 
American  Modification  of  Closed  Circuit,  214. — Comparative  Ad- 
vantages of  Different  Plans,  215. — Position  of  Battery  in  Closed 
Circuit,  216. — General  Considerations  respecting  Telegraphic  Cir- 
cuits, 217. — Relation  of  Conductivity  to  Insulation  Resistance,  218. 
— Effect  of  Imperfect  Insulation,  219. — Working  Efficiency  of  Tele- 
graphic Circuit,  220. — Telegraphic  Conductors,  221, — Iron  Wires, 


xii  Contents. 


PAGE 


222. — Office  Wires,  223.— Copper  Line  Wires,  224. — Telegraphic 
Line  Insulators,  225. — Defects  of  Glass  Insulator,  226. — Resistance 
Influenced  by  Form  of  Insulator,  227. — Hard  Rubber  Insulator, 
228. — Paraffin  Insulator,  229. — Porcelain  Insulator,  230. — Defective 
Insulation  of  American  Lines,  231,  232,  233. — Distribution  of  Po- 
tentials in  Telegraphic  Circuits,  234. — Potential  in  Perfectly  Insu- 
lated Circuit,  235. — Determination  of  Potential  by  Calculation, 
236. — Potentials  within  the  Battery,  237,  238,  239,  240. — Potentials 
in  Imperfectly  Insulated  Circuit,  241. — Effect  of  Imperfect  Insula- 
tion upon  Flow  of  Current,  242. — Resistance  and  Current  in  Leaky 
Lines,  243. — Computation  of  Working  Efficiency  of  Line,  244,  245. 
— Effect  of  Position  of  Fault,  246. — Best  Position  of  Batteries  in 
Circuit,  247. — Intermingling  of  Currents  on  Different  Lines,  248. — 
Remedy  for  Cross-Current,  249,  250. — Value  of  Poles  and  Cross- 
Arms  as  Insulators,  251. — Tests  of  Resistance  of  Cross-Arms,  252. 
— Tests  of  Glass  Insulators,  253. — Importance  of  High  Working 
Efficiency,  254. — Best  Method  of  Improving  Efficiency,  255,  256...  102 

CHAPTER     VIII. 

EQUIPMENT   OF    AMERICAN    TELEGRAPH    LINES. 

Apparatus  Essential  in  Telegraphy,  §  257. — Construction  of  Key,  258. 
— Modifications  of  Key,  259. — Adjustment  of  Key,  260. — Sounder, 
261. — Short  Line  Instrument,  262. — Adjustment  of  Sounder,  263. — 
Pocket  Apparatus,  264. — Box  Sounder,  265. — Working  by  Relay 
and  Local  Circuit,  266. — Construction  of  Relay,  267. — Adjustments 
of  Relay,  268. — Register,  269,  270. — Adjustments  of  Register,  271. 
— Causes  of  Defective  Marking,  272. — Ink-Writing  Register,  273. 
— Circuits  of  American  System,  274. — Arrangements  of  Apparatus 
at  Way-Station,  275. — Connections  of  Apparatus  of  Way-Station, 
276. — Manipulation  of  Switchboard,  277. — Testing  for  Disconnec- 
tion, 278. — Reporting  Result  of  Test,  279. — Wedge  Cut-Out,  280. — 
Multiple  Wire  Switchboard,  281. — Multiple  Spring-Jack,  282. — Uni- 
versal Switchboard,  283. — Manipulation  of  Universal  Switchboard, 
284. — Arrangement  of  Apparatus  of  Terminal  Station,  285. — Ter- 
minal Switchboard,  286. — Instrument  Tables,  287. — Lightning  Ar- 
rester, 288. — Plate  Arrester,  289.— Safety  Fuse,  290. — Inspection 
and  Care  of  Arresters,  291. — Repeater,  292. — Manual  and  Automatic 
Repeaters,  293. — Button  Repeater,  294. — Wood's  Repeater,  295. — 
Management  of  Button  Repeater,  296. — Milliken  Automatic  Re- 
peater, 297. — Management  of  Automatic  Repeaters,  298. — Dynamo- 
Electric  Generator,  299. — Characteristics  of  Dynamo-Current,  300. — 
Electro-Magnetic  Field,  301. — Commutator,  302. — Characteristics 
of  Dynamo,  303.  —  Dynamo  in  Potential  Series,  304.  —  Positive 
and  Negative  Dynamo  Series,  305. — Arrangement  of  Shunt  Coils, 
306. — Capacity  of  Dynamo  Generator,  306^. — Multiple  Telegraphy, 
307. — Differential  Electro-Magnet,  308. — Construction  of  Differen- 
tial Magnet,  309. — Single-Current  Duplex,  310. — Circuits  of  Single- 


Contents.  xiii 

PACK 

Current  Duplex,  311. — Artificial  Line,  312. — Balancing  Resistance, 
313. — Electrostatic  Capacity  of  Line,  314. — Electrostatic  Accumu- 
lation upon  Insulated  Conductor,  315. — Effect  of  Currents  of 
Charge  and  Discharge,  316. — Condenser,  317. — Ground  and  Spark 
Coils,  318. — Double-Current  Duplex,  319. — Quadruplex,  320. — 
Principle  of  Diplex,  321,  322. —  Operation  of  Diplex,  323. — Diplex 
and  Contraplex  Combined,  324. — Quadruplex  worked  by  Dynamo- 
Currents,  325. — Distribution  of  Currents  in  Quadruplex  Apparatus, 
326,  327. — Practical  Management  of  Quadruplex,  328. — Adjustment 
of  Apparatus,  329. — Repeaters  for  Multiple  Telegraph  Systems, 
329* 138 

CHAPTER     IX. 

TESTING   TELEGRAPH    LINES. 

Object  of  Tests,  §  330. — Faults  and  Interruptions,  331. — Testing  for 
Disconnection,  332,  333.— Testing  for  Partial  Disconnection,  334. — 
Testing  for  Escape,  335.— Testing  for  Cross,  336.  — Principle  of 
Cross  Test,  337,  338,  339. — Testing  by  Quantitative  Measurement, 
340. — Wheatstone  Bridge,  341. — Best  Ratio  of  Electromotive  Forces 
and  Resistances,  342. — Principle  of  Wheatstone  Bridge,  343. — Act- 
ual Construction  of  Bridge,  344. — Galvanometer  for  Wheatstone 
Bridge,  345. — To  Measure  the  Conductivity  Resistance  of  a  Tele- 
graph Line,  346. — Conductivity  Resistance  by  Loop  Method,  3463. 
— Earth  Currents,  347. — Measurement  of  Resistance  of  Ground 
Plate  at  Distant  Station,  348.  — Measurement  of  Insulation  Resist- 
ance of  Line,  349. — Location  of  Position  of  a  Ground,  350. — Loca- 
tion of  Position  of  an  Escape,  351. — Method  of  Double  Measure- 
ment, 352. — Loop  Test,  353. — Varley's  Loop  Test.  354. — To  Locate 
a  Cross,  355,  356,  357. — To  Locate  a  Bad  Joint  or  Abnormal  Resist- 
ance, 358. — Measurement  of  very  High  Resistances,  359. — Shunts 
of  Galvanometers,  360. — Measurement  by  Deflections,  361. — Meas- 
urement of  Resistance  of  Insulators,  362. — Measurement  of  In- 
ternal Resistance  of  Battery,  363,  364. — Measurement  of  Resistance 
of  Galvanometer,  365. — Differential  Galvanometer,  366. — Testing 
for  Insulation  by  Received  Currents,  367. — Use  of  Voltmeter  and 
Ammeter  in  Telegraphic  Testing,  368. — The  Weston  Ammeter 
and  Voltmeter,  369. — Recording  Tests  of  Conductivity  and  Insula- 
tion, 370 190 

CHAPTER     X. 

HINTS      TO      LEARNERS. 

Formation  of  the  Telegraphic  Code,  §  371. — The  American  Morse  Code, 
372. — Learning  the  Code,  373. — Handling  the  Key,  374. — Element- 
ary Principles  of  Code,  375. — Preliminary  Practice  with  the  Key, 
376. — Exercises  upon  Code  Characters,  377. — Reading  by  Sound, 
378,  379. — A  Parting  Word,  380 216 


LIST    OF    TABLES. 


PAGE 

I.  CHEMICAL  ATOMIC  WEIGHTS   OF   ELEMENTARY   SUBSTANCES   OP 

BATTERIES 8 

II.  SPECIFIC  GRAVITIES  OF  BATTERY  SOLUTIONS 9 

III.  NATURAL  TANGENTS  FOR  EVERY  HALF  DEGREE 55 

CONDUCTORS  AND  INSULATORS  IN  RELATIVE  ORDER 57 

IV.  SPECIFIC  RESISTANCES  OF  VOLTAIC  SOLUTIONS 63 

V.  RECIPROCALS  OF  NUMBERS  FROM  i  TO  100 67 

VI.  SYNOPSIS  OF  PRACTICAL  UNITS 73 

VII.  CHEMICAL  EQUIVALENTS  OF  BATTERY  MATERIALS. 75 

VIII.  DIMENSIONS  AND  PROPERTIES  OF  COPPER  MAGNET  WIRES 94 

IX.  SIZE,  WEIGHT,  AND  RESISTANCE  OF  TELEGRAPH  WIRES 112 

X.  RESISTANCES    AND    ESCAPE    UPON    LEAKY    LINES    OF    VARIOUS 

LENGTHS 129 

XL  FARMER'S  TABLE  FOR  COMPUTING  FLOW  OF  CURRENT  IN  LEAKY 

LINES 137 

THE  MORSE  TELEGRAPHIC  CODE .  218 


MODERN    PRACTICE 


OF   THE 


ELECTRIC  TELEGRAPH. 


CHAPTER   I. 

INTRODUCTORY. 

1.  Fundamental   Principles. — The  electric   telegraph  is  an 
apparatus  by  means  of  which  physical  effects  may  be  instantaneously 
produced  in  distant  places.     Such   effects  are   technically  termed 
signals. 

2.  The  art  of  electric  telegraphy  consists  in  the  production,  control, 
and  organization  of  electric  signals.     The  signals  employed  in  teleg- 
raphy may  be  either  visible  or  audible.      Visible  signals  may  be 
either  evanescent,  as  in  the  needle  telegraph  used  in  Great  Britain, 
and  in  some  forms  of  apparatus  employed  in  working  long  submarine 
cables,  or  permanent ',  as  in  the  case  of  the  Morse  register,  and  in  the 
instruments  used  on  submarine  cables  of  comparatively  moderate 
length.     Audible  signals  are  produced  by  the  sounder,  and  some 
other  less  common  forms  of  apparatus. 

3.  The    signals   which    are    utilized   in   electric   telegraphy   are 
produced   at  a  distant  point  as  required  by  the  agency  of  elec- 
tricity. 

4.  Nature  of  Electricity. — We  do  not  as  yet  know  ;  perhaps 
we  never  shall  know  with  certainty,  what  the  agent  we  call  electricity 
really  is.     Formerly  it  was  assumed  to  be  an  imponderable  fluid. 
This  hypothesis  was   suggested   by   Franklin.      In   later  years  it 
gradually  came  to  be  regarded  as  one  of  the  many  different  forms  of 
energy,  or,  in  other  words,  as  a  peculiar  affection  of  the  particles  of 
ordinary  matter.     Recent  scientific  opinion  shows  a  marked  tendency 


2  Introductory. 

toward  the  acceptance  of  the  old  hypothesis  of  a  fluid,  in  a  modi- 
fied form. 1 

This  conception  of  the  essential  nature  of  electricity  appears  to  be  the 
logical  outgrowth  of  the  opinions  held,  more  or  less  definitely,  by  such  phi- 
losophers as  Franklin,  Cavendish,  Faraday,  Henry,  Thomson,  and,  more 
especially,  Clerk-Maxwell.  The  theoretical  side  of  the  question  is  discussed 
with  great  ability  by  Oliver  J.  Lodge,  in  his  Modern  Views  of  Electricity, 
while  its  latest  aspects  are  summarized  in  a  valuable  paper  by  Professor 
William  A.  Anthony:  "A  Review  of  Modern  Electrical  Theories,"  Electrical 
Engineer,  ix.  43  ;  Trans.  Am.  Inst.  Elec.  Eng.,  vii.  33. 

For  practical  purposes,  however,  it  is  fortunately  not  in  the  least 
necessary  that  we  should  know  what  electricity  is,  nor  that  we  should 
commit  ourselves  to  any  particular  assumption  as  to  its  essential 
nature.  A  thorough  knowledge  of  the  physical  effects  which  it  is 
capable  of  producing  under  different  conditions,  and  of  the  laws 
which  govern  its  action,  are  all  that  the  practical  electrician  needs 
to  acquire. 

5.  Elements  of  the  Electric  Telegraph. — An  electric  tele- 
graph comprises  four  essential  elements.  These  are  as  follows : 

(i)  Means  for  setting  in  action,  or,  as  it  is  commonly  termed,  producing, 

electricity,  termed  the  generator. 
(ii)  Means  for  conducting  the  electricity  from  place  to  place,  termed  the 

conductor  or  conducting  circtiit. 

(iii)  Means  for  controlling  the  flow  of  electricity  for  the  purpose  of  pro- 
ducing signals,  termed  the  transmitter. 
(iv)  Means  for  indicating  or  recording  signals,  termed  the  receiver. 

1  Electricity  and  magnetism  are  not  forms  of  energy ;  neither  are  they  forms  of 
matter.  They  may,  perhaps,  be  provisionally  defined  as  properties  or  conditions  of 
matter ;  but  whether  this  matter  be  the  ordinary  matter,  or  whether  it  be,  on  the  other 
hand,  that  all-pervading  ether  by  which  ordinary  matter  is  everywhere  surrounded,  is 
a  question  which  has  been  under  discussion,  and  which  may  now  be  fairly  held  to  be 
settled  in  favor  of  the  latter  view.— DANIELL  :  Principles  of  Physics  [zd  ed.],  532. 


CHAPTER   II. 

SOURCES    OF    ELECTRICITY. 

6.  Origin  of  Electricity. — Electricity,  or,  more  properly,  elec- 
trical action,  may  be  produced  in  several  known  ways.  Although 
electricity,  whatever  may  be  its  origin,  is  demonstrably  one  and  the 
same  thing,1  it  has  nevertheless  become  customary  to  speak  of  it 
conventionally,  under  different  names,  indicative  of  its  origin.  Thus, 
we  have,  principally : 


(a)  CHEMICAL  ELECTRICITY. 

(b)  MAGNETO-ELECTRICITY. 


(c)  FRICTIONAL  ELECTRICITY. 

(d)  THERMO-ELECTRICITY. 


There  are  other  means  of  producing  electrical  manifestations, 
which  have  as  yet  no  practical  utility  for  the  purpose  under  consid- 
eration, and  need  not  be  further  considered  here.  Of  those  which 
have  been  specifically  mentioned,  chemical  and  magneto-electricity  only, 
have  proved  by  experience  to  be  adapted  to  the  requirements  of 
the  art  of  telegraphy. 

7.  Chemical  Electricity. — The  effects  of  electricity  are  most 
conveniently  studied   in   connection  with  that  form  which  has  its 
origin  in  chemical  decomposition,  especially  as  it  is  by  the  agency 
of  chemical  electricity  that  nearly  all  the  telegraphic  apparatus  of 
the  world  is  operated, 

8.  The  Voltaic  Element. — The  electricity  which  is  employed 
in  telegraphy  is  usually  derived  from  one  or  more  batteries,  each  of 
which  is  composed  of  a  greater  or  less  number  of  cells  connected 
Together  in  a  series.     A  single  cell  is  termed  a  voltaic  or  galvanic 
element. 

9.  Description  of  the  Typical  Cell. — The   active   or   actu- 
ating parts  of  each  element  consist  in  practice  of  two  dissimilar 

metals,  each  of  which  is  immersed  in  a  different  chemical  solution. 

• 

1  This  fact  was  first  experimentally  established  by  Faraday  in  1832.  His  account 
of  this  investigation  is  very  instructive,  and  is  given  at  length  in  his  Experimental 
Researches  (third  series),  vol.  i.  pp.  76-109. 

3 


Sources  of  Electricity. 


The  following  will  serve  to  explain  the  construction  most  usually 
employed  in  telegraphy : 

In  Fig.  i  is  represented  a  cylindrical  glass  jar,  7  in.  in  height, 
6  in.  in  diameter,  and  weighing  about  2.5  Ibs. 


FIG.  i.    Separate  parts  of  Gravity  Cell. 

At  the  right  of  this  is  a  mass  of  zinc  weighing  about  3  Ibs.,  which 
has  been  cast  in  an  iron  mould  in  the  form  represented.  It  is  pro- 
Tided  with  a  hanger  by  means  of  which  it  may  be  suspended  from 
the  upper  edge  of  the  jar,  and  also  with  a  damp-screw  by  means  of 
which  a  metallic  wire  may  be  securely,  but  removably,  attached  to  it. 

At  the   left  of  the  jar   is   seen   a   triple   plate   of   thin   rolled 
copper,  spread  out  laterally  into  the  form  shown,  which   is 
designed  to  be  placed  in  the  bottom  of  the  glass  cell.     Each 
separate  plate  may  be  cut  in  the 
form  shown  in  Fig.  2,  the  three 
being  then    united  by  a  single 
copper  rivet  at  the  middle,  and 
the   free   ends  separated    radi- 
ally, as  in  Fig.  i,  before  placing 
in  the  jar. 

A  vertical  copper  wire «is  permanently  riveted  to  the  copper  plate. 
It  must  not  be  soldered.  The  wire  is  made  long  enough  to  extend 
some  6  in.  or  7  in.  above  the  top  of  the  jar.  It  passes  loosely 
through  the  bore  of  a  small  glass  tube,  the  reason  for  which  is  here- 


FIG.  a.    Section  of  Copper  Plate. 


Phenomena  of  the  Cell. 


after  explained  (27).  It  is  provided  at  its  upper  end  with  a  brass  clamp 
termed  the  copper-connector.  Instead  of  using  a  glass  tube,  it  is  quite 
usual  to  substitute  a  piece  of  wire  covered  with  a  coating  of  gutta-percha, 
india-rubber,  or  other  flexible  material  impervious  to  the  solution. 

The  particular  form  of  copper-connector  shown  in  the  figure  con- 
sists of  a  short  cylindrical  piece  of  brass,  perforated  with  a  longi- 
tudinal hole  for  receiving  the  ends  of  the  wires,  into  which  enter 
transverse  .  thumb  -  screws  for 


FIG.  3.    Copper-connector. 


clamping  the  wire.    A  longitudi- 
nal cross-section  of  this  device    1= 
is  shown  in  Fig.  3. 

10.    Each  element,  when  com- 
plete, consists  of  the  several  parts  described,  assembled  together  in 
the  relation  shown  in  Fig.  4,  which  also  shows  the  jar  filled  with 
water  to  within  i  in.  of  the  top.     Care  must  be  observed,  in  hang- 
ing the  zinc,  not  to  fracture  the  glass  jar. 

It  is  very  essential  that  the  water  for  charging  a  voltaic  element 
should  be  both  pure  and  soft.  Impure  or  hard  water  obstructs,  and 
sometimes  altogether  prevents,  the  proper  action  of  the  chemicals. 

Clean  rain-water,  if  it  can 
be  procured,  is  best  for  the 
purpose. 

n.  Phenomena  of 
the  Cell.— If  a  cell,  hav- 
ing been  thus  filled  with 
water,  in  which  zinc  and 
copper  plates  are  im- 
mersed, as  shown  in  Fig. 
4,  be  permitted  to  stand 
undisturbed  for  a  consid- 
erable time,  a  collection 
of  minute  bubbles  will  be 
observed  clinging  to  the 
surface  of  the  zinc  plate, 
but  no  such  effect  will  be 
observed  upon  the  copper. 
These  bubbles  contain 
hydrogen  gas,  and  are  the 
result  of  a  chemical  reaction  which  takes  place  between  the  water 
and  the  zinc. 

12.  Water  is  made  up  of  two  parts  of  hydrogen  and  one  part  of 
oxygen,  held  together  by  chemical  affinity.  In  the  present  case,  a 


FIG.  4.    Gravity-cell  ready  for  Service. 


6  Sources  of  Electricity. 

certain  portion  of  the  oxygen  of  the  water  enters  into  chemical  com- 
bination with  the  metal,  forming  the  compound  termed  oxide  of  zinc. 
A  thin  coating  of  this  oxide  ultimately  covers  the  surface  of  the  zinc 
plate,  giving  it  a  dull  bluish  gray  color,  and  preventing  further  oxidi- 
zation. At  the  same  time  the  hydrogen  which  was  associated  with 
the  oxygen  in  the  decomposed  water,  is  set  free,  and  collects  in 
bubbles  which  adhere  to  the  surface  of  the  zinc  plate.  When  these 
bubbles  are  detached  they  rise  to  the  surface  of  the  water  and  the 
contained  hydrogen  escapes  into  the  air.2 

13.  This  process   of  oxidization   will  be  recognized  as  identical 
with  that  which  takes  place  in  the  rusting  of  iron  when  exposed  to 
the  action  of  moisture.     It  is  also  the  same,  from  a  chemical  point 
of  view,  as   the  process  of  combustion  or  burning.     No  perceptible 
effect  is  produced  upon  the  copper,  because  the  oxygen  has  less  affin- 
ity for  this  metal  than  it  has  for  hydrogen,  and  hence  has  no  tend- 
ency to  separate  from  the  water. 

14.  Chemistry  of  the  Voltaic  Effect.— If  now  a  small  quan- 
tity of  sulphuric  acid  were  to  be  added  to  the  water  contained  in  the 
jar,  and  at  the  same  time  the  zinc  and  copper  be  joined  together 
by  a  metallic  wire  in  the  air  outside  the  jar,  a  much  more  vigorous 
chemical   action   will   immediately  set  in.     The   dissolution   of  the 
zinc  in  the  liquid  will  go  on  with  increased  rapidity,  attended  with 
the  evolution  of  hydrogen  in  bubbles,  not  as  before  upon  the  surface 
of  the  zinc,  but  upon  the  copper. 3 

15.  Although  the   chemical   action  in  the  case  just  supposed  is 
attended  by  the  development  of  electricity,  yet  such  an  organization, 
as  a  generator  of  electricity  for  telegraphic  purposes, -would  be  of 
little  practical  utility.     The  chemical  action,  though  vigorous  at  first, 
quickly  falls  off,  and  in  a  short  time  nearly  or  quite  ceases.     This 
effect  arises  from  the  adherence  of  the  liberated  hydrogen  to  the  sur- 

3  In  a  chemical  compound  the  qualities  of  the  constituents  are  wholly  merged  in 
those  of  the  product,  and  this  circumstance  distinguishes  a  true  compound  from  a 
mechanical  mixture  in  which  the  qualities  of  each  ingredient  are  to  a  greater  or  less 
extent  preserved.  .  .  .  Chemical  combinations  always  take  place  in  certain 
definite  proportions,  either  by  weight  or  measure.  .  .  .  The  atomic  theory  sup- 
poses that  two  atoms  of  hydrogen  combine  with  one  atom  of  oxygen  to  form  a  mole- 
cule of  water,  and  since  each  atom  of  oxygen  weighs  16  times  as  much  as  an  atom  of 
hydrogen,  the  two  substances  must  combine  in  the  proportion  of  2  : 16,  or  i :  8.  This 
principle  is  known  in  chemistry  as  the  law  of  definite  proportion.— COOKE  :  New  Chem- 
istry^ 104-8. 

3  The  chemical  reaction  is  as  follows  : — Sulphuric  acid  is  composed  of  hydrogen  2 
parts,  sulphur  i  part,  oxygen  4  parts  ;  in  chemical  notation  (H»  SO).  The  sulphur 
and  oxygen  unite  with  the  zinc,  forming  sulphate  of  zinc,  composed  of  zinc  i  part, 
sulphur  i  part,  and  oxygen  4  parts  (Zn  SO4),  which  remains  in  solution  in  the  water, 
while  the  hydrogen  is  set  free  at  the  copper  plate. 


The  Hydrometer. 


face  of  the  copper,  preventing  contact  of  the  solution  therewith. 
This  gas  also  reacts  upon  the  sulphate  of  zinc  (s.  z.)  which  permeates 
the  solution,  and  causes  its  zinc  constituent  to  be  deposited  upon  the 
copper.  For  these  reasons  it  is  necessary  to  dispose  of  the  hydrogen 
in  such  a  way  that  interfering  actions  may  be  avoided.  This  is  effected 
in  practice  by  immersing  the  copper  and  zinc  in  different  solutions. 

16.  The    Gravity    Cell. — In    the    voltaic    element   which    has 
been  described  and  shown   in  Fig.  4,  the  two  solutions  are  of  un 
equal  densities,  so  that  one  can  be  made  to 

float,  as  it  were,  upon  the  other,  in  the 
same  manner  that  oil  floats  upon  water. 
Hence  it  has  received  the  name  of  the 
gravity  cell. 

17.  Specific  Gravity. — The  density  or 
weight  of  a  given  bulk  of  any  liquid  com- 
pared with  that  of  pure  water  is  termed  its 
specific  gravity  (s.  g. )     The  s.  g.  of  a  liquid  is 
numerically  expressed  in  decimals  or  mixed 
numbers,    pure   water    being   taken    as    the 
standard  or  unity.     For  example,  the  s.  g.  of 
water  being  i.oo,  that  of  linseed  oil  is  0.93, 
while  that  of  commercial  sulphuric  acid  is 
1.84,  and  of  mercury  13.58. 

18.  The    Hydrometer.— The  s.  g.  of 
any  liquid  may  be  determined  with  sufficient 
accuracy  for  ordinary  purposes  by  means  of 
the  hydrometer,  shown  in  Fig.  5,  which  con- 
sists of  a  hollow  glass  float,  weighted  below 
with   shot,  and  carrying  a  stem  at  the  top 
provided  with  a  graduated  scale.     When  the 
hydrometer  is  made  to  float  in  any  liquid, 
the  division  of  the  scale  at  the  surface  de- 
notes its  s.    .4 


FIG.  5.  Baume's  Hydrometer. 


19-   Charging  the  Cell. — The  glass  jar  shown  in  Fig.  4,  which 

*  The  arbitrary  scale  of  the  hydrometer  commonly  known  as  Baume's,  is  deter- 
mined as  follows  : — The  point  to  which  the  instrument  sinks  in  pure  water  is  assumed 
as  o°  (zero),  while  15°  is  at  the  point  to  which  it  sinks  in  a  solution  containing  15  parts 
by  weight  of  common  salt  in  85  parts  of  water.  This  space  is  divided  into  15  equal 
parts,  and  equivalent  graduations  are  continued  to  any  desired  extent.  The  most 
useful  scale  for  testing  the  s.  g.  of  battery  solutions  is  one  having  a  stem  about  2  inches 
long,  graduated  in  degrees  from  15°  to  40°.  These  degrees  denote  the  percentage  of 
common  salt  in  a  solution ;  but  do  not  correspond  exactly  with  the  percentages  in 
battery  solutions,  as  will  appear  from  an  examination  of  the  tables  in  (23). 


8  Sources  of  Electricity. 

is  7  in.  high  and  6  in.  in  diameter,  is  intended  to  contain  7  Ibs.,  or  0.84 
U.  S.  gallons  of  liquid  ;  and  this  quantity,  when  the  copper  and  zinc 
plates  are  in  place,  will  fill  it  to  within  about  one-half  inch  of  the  top. 
A  smaller  size  of  cell  (6  in.  x  5  in.),  is  also  kept  in  stock  by  dealers. 

20.  To  charge  the  cell,  prepare  separately  a  sufficient  quantity  of 
the  zinc  and  of  the  copper  solutions.     For  the  zinc  solution,  which 
may  be  mixed  in  the  jar,  take  for  each  cell : 

Pure  soft  water,  by  weight,  91  oz.  (i£  pints). 
Crystallized  sulphate  of  zinc  (white  vitriol),  10  oz. 

Dissolve,  and  let  the  solution  stand  for  some  hours.  The  s.  g.  of 
the  solution  should  be  i.io. 

21.  It  is  not  absolutely  necessary  to  make  use  of  s.  z.  in  setting 
up  the  cell.     If  pure  water  be  substituted  for  the  solution  directed 
to  be  used  in  the  last  paragraph,  and  the  circuit  be  closed  between 
its  poles,  which  is  technically  termed  short-circuiting  the  cell  (14), 
sufficient  s.  z.  will  be  formed  within  a  day  or  two  to  bring  it  into  full 
action.     Many  electricians  are  of  the  opinion  that  a  cell  started  in 
this  way  will  remain  in  good  condition  for  a  longer  time   than  if 
charged  with  a  mechanically-mixed  zinc  solution. 

22.  Copper  and  Zinc  Solutions. — For  the  copper  solution, 
take  in  another  glass  vessel,  for  each  cell : 

Pure  soft  water,  by  weight,  42  oz.  (2^  pints). 
Crystallized  sulphate  of  zinc,  4  oz. 
Crystallized  sulphate  of  copper,  8  oz. 

The  following  table  will  be  found  convenient  for  reference : 

TABLE     I. 

CHEMICAL    ATOMIC    WEIGHTS    OF    ELEMENTARY    SUBSTANCES    OF 

BATTERIES. 


SUBSTANCE. 

SYMBOL. 

ATOMIC   WEIGHT. 

Copper 

Cu 

5"!    A 

Zinc     

Zn 

6^.2 

Sulphur          

s 

•32.  0 

Oxvsren 

o 

16  o 

Hydrogen  

H 

i  .0 

The  chemical  notation  for  crystallized  sulphate  of  copper  is  (Cu. 
It  is  composed  of 

Metallic  Copper 25.4  per  cent. 

Sulphur 12.8       " 

Oxygen 57.7 

Hydrogen  4.0       " 


Specific  Gravities  of  Battery  Solutions. 


The  chemical  notation  of  crystallized  sulphate  of  zinc  is  (Zn  SO*  7H8O). 
It  is  composed  of 

Metallic  Zinc 22.7  per  cent. 

Sulphur ii. i       " 

Oxygen 61.3       " 

Hydrogen 4.9       ' ' 

When  dissolved,  the  s.  c.  solution  will  be  of  a  beautiful  dark  blue 
tint,  and  its  s.  g.  will  be  1.21. 

23.  Specific  Gravities  of  Battery  Solutions. — The  follow- 
ing tables  will  aid  in  maintaining  cells  is  good  condition : 

TABLE    II. 

SPECIFIC  GRAVITIES  OF  BATTERY  SOLUTIONS. 
ZINC. 


S.  g.  of  solution  at 
77°  Fab. 

Reading  by  Baume 
hydrometer. 

Per  cent  of  crystal- 
lized s.  z.  in  solution. 

REMARKS. 

.11 

15 

IS-? 

Minimum  density. 

.12 

16 

16.8 

•13 

17 

17.9 

•135 

18 

18.9 

.14 

19 

20.0 

•15 

20 

21.  1 

Maximum  density. 

.16 

21 

22.3 

•17 

22 

23-4 

.18 

23 

24.6 

.19 

24 

25.8 

.20 

25 

26.9 

.46 

48 

62.1 

Saturation. 

COPPER. 


S.  g.  of  solution  at 
72°  Fah. 

Reading  by  Baume 
hydrometer. 

Per  cent,  of  crystal- 
lized s.  c.  in  solution. 

REMARKS. 

1.03 

5 

5-0 

1.07 

10 

IO.O 

I.  II 

15 

15.4 

Half  saturation. 

I-I5 

20 

21.2 

1.20 

25 

27-5 

1.  21 

27 

3O.O 

Saturation. 

24.  Installation  of  the  Gravity  Cell. — The  copper  and  zinc 
plates  being  put  in  their  respective  places  in  the  jar  (which  will  then 
4>e  about  three-fourths  full  of  s.  z.  solution),  the  heavier  s.  c.  solution 


io  Sources  of  Electricity. 

may  be  introduced  into  the  bottom  by  means  of  a  f  in.  tube  of  glass 
or  rubber,  having  a  small  glass  or  rubber  funnel  inserted  in  its  upper 
end.  The  lower  end  of  the  tube  must  be  central  and  very  near  the 
bottom,  and  the  s.  c.  must  be  poured  in  quite  slowly,  so  as  not  to 
agitate  the  mass  and  cause  the  two  solutions  to  mingle.  If  this 
operation  is  carefully  performed,  the  lower  part  of  the  jar  will  now 
be  filled  with  s.  c.  solution,  of  a  uniform  deep  blue  color,  to  a  point 
a  little  above  the  top  of  the  copper  plate,  being  separated  from  the 
transparent  s.  z.  solution  above  by  a  sharply  defined  line  of  demarka- 
tion.  Care  must  now  be  taken  that  the  cell  is  not  moved  about,, 
shaken,  or  stirred  by  the  careless  removal  of  the  zinc  or  copper 
plates,  as  this  would  cause  the  two  solutions  to  intermingle,  a  con- 
dition which  it  is  very  necessary  to  avoid.  For  the  same  reason,  it 
is  advisable  to  place  each  cell  in  the  position  which  it  is  to  perma- 
nently occupy,  before  introducing  the  s.  c.  solution.  The  most 
convenient  place  will  be  found  to  be  a  shelf  about  48  in.  from  the 
floor.  An  enclosed  box  affixed  to  a  wall  or  frame,  and  having  a 
glass  front  hinged  to  open  upward,  is  an  excellent  arrangement,  as 
the  cells  are  then  in  sight,  so  that  their  condition  may  be  observed 
at  all  times,  while  at  the  same  time  they  are  protected  from  dirt,, 
and  in  a  great  measure  from  evaporation  and  from  extremes  of 
temperature.5 

25.  Instead  of  mixing  the  s.  c.  solution  in  a  separate  vessel,  it  is  a 
common  practice  to  fill  the  jar  to  within  i  inch  of  the  top  with  the 
s.  z.  solution,  prepared   as  above  directed,  and  then   slowly  drop  in 
8  oz.  of  s.  c.  crystals  about  the  size  of  a  hazel-nut,  which  will  fall  to- 
the  bottom  and  slowly  dissolve.     The  only  objection   to  this  pro- 
cedure is  its  liability  to  form  a  s.  c.  solution  of  unequal  density  in  dif- 
ferent parts,  which  is  undesirable  (26).     When  this  plan  is  adopted, 
care  must  be  taken  not  to  put  in  more  than  the  prescribed  quantity 
of  s.  c.,  and  particularly  to  see  that  no  particle  of  it  gets  upon  the 
zinc  plate. 

26.  Modified  Form  of  the  Copper  Plate.— A  more  advan- 
tageous form  for  the  copper  plate  than  that  which  has  been  described, 

6  Wooden,  tin,  or  porcelain  covers  are  sometimes  fitted  to  the  cells  for  excluding 
dust  and  preventing  evaporation,  and  serve  a  good  purpose.  Wooden  covers  should 
not  fit  too  closely ;  there  is  danger  that  they  may  swell  from  moisture  and  fracture 
the  jars. 

Great  annoyance  is  sometimes  caused  by  the  apparently  unaccountable  breakage  of 
glass  jars.  The  primary  cause  of  this  is  poor  material  or  imperfect  annealing  during 
the  process  of  manufacture  ;  the  immediate  cause  is  usually  a  sudden  change  of  tem- 
perature. A  jar  on  a  high  shelf  in  a  warm  room  in  winter  is  sometimes  cracked  by  the 
current  of  cold  air  caused  by  opening  an  outer  door.  A  little  care  will  avoid  such 
accidents. 


Formation    of  the    Electric    Circuit.  1 1 

particularly  in  case  it  is  desired  to  maintain  a  current  of  moderate 
quantity  for  a  long  time,  is  a  ribbon  of  very  thin  rolled 
copper,  48  in.  long  and  J  in.  wide,  coiled  spirally  like  a 
clock-spring,  and  laid  flat  in  the  bottom  of  the  cell,  the  con- 
ducting wire  being  riveted  to  the  outer  end  as  seen  in  Fig.  6. 
An  objection  to  the  form  of  plate  shown  in  Fig.  4,  when 
used  under  the  conditions  here  mentioned,  is  that  unless 
carefully  looked  after,  the  s.  c.  solution  will 
become  weaker  at  the  top  than  at  the  bot- 
tom of  the  copper,  whereupon  a  closed  cir- 
cuit (30)  is  established,  consisting  of  one 
FIG.  6.  Modification  of  Copper  metal  (the  copper),  and  two  dissimilar 
liquids  (the  strong  and  the  weak  solu- 
tion), setting  up  an  action  which  is  liable  to  attack  and  destroy  the 
upper  portion  of  the  plate,  uselessly  consuming  material  for  which 
no  equivalent  external  current  is  rendered. 

27.  This  action  explains  the  necessity  of  enclosing  the  connecting 
wire  from  the  copper  electrode  of  the  gravity  battery  in  a  glass  tube, 
or  covering  it  with  gutta-percha  or  india-rubber,  where  it  is  exposed 
to  the  action  of  the  solution.     If  it  were  not  protected  it  would  soon 
be  destroyed  by  chemical  action,  and  the  circuit  consequently  inter- 
rupted. 

28.  Formation  of  the  Electric  Circuit.— The  parts  of  the 
cell  being  properly  assembled  together,  and  the  solutions  in  their 
respective  places  as  directed  in  (24),  the  element  is  ready  for  service. 
If  now  the  zinc  and  copper  plates  be  joined  together  in  the  air  by  a 
metallic  wire  as  before  explained  (14),  a  current  of  electricity,  as  it  is 
technically  termed,  will  traverse  the  wire.     It  wilt  traverse,  moreover, 
not  only  the  wire,  but  also  the  metallic  plates  and  solutions  within 
the  voltaic  element,  the  whole  path  forming  what  is  termed  a  circuit 
of  electrical  conductors,  or  briefly,  an  electric  circuit. 

29.  The  presence  of   an  electric  current  in  such  a  circuit  may 
be  demonstrated  in  several  different  ways,  as  will  be  shown  further 
on  (86).     For  the  present  we   are  only  concerned   to  observe  its 
immediate  effects  upon  the  constituent  parts  of  the  voltaic  element 
which  sets  it  in  action. 

30.  The  circuit  of  a  voltaic  element  maybe  diagrammatically  rep- 
resented by  a  closed  ring  as  shown  in  Fig  7.     It  is  composed  of  the 
following  parts : — 


(i.)  The  zinc  plate. 
(2.)  The  zinc  solution. 
(3.)  The  copper  solution. 


(4.)  The  copper  plate. 

(5.)  The  metallic  connecting  wire. 


12 


Sources  of  Electricity. 


POSITIVE 


The  four  first  named  constitute  the  internal  circuit,  and  the  last 
the  external  circuit. 

Before  the  zinc  and  copper  plates  are  united  by  the  connecting 
wire,  the  circuit  is  said  to  be  open  or  broken,  and  the  cell  is  said  to  be 

on  open  circuit.  When  the 
connection  is  established  by 
the  wire,  the  circuit  is  said 
to  be  made,  completed,  or 
LPOLE  closed,  the  last  mentioned 
phrase  being  most  usual. 
In  this  case  the  cell  is 
spoken  of  as  being  on  closed 
circuit,  which  is  another  way 
of  saying  that  chemical  ac- 
tion is  going  on  within  it. 

31.  Nomenclature  of 
the  Electric  Circuit— 
In  a  voltaic  cell,  the  zinc 


FIG.  7.    Diagram  of  Closed  Voltaic  Circuit 


plate  is  termed  the  positive  plate  or  element,  and  the  copper  the 
negative  plate  or  element.  These  terms  are  purely  conventional 
and  arbitrary,  and  properly  signify  nothing  beyond  the  antagonis- 
tic or  opposite  electrical  condition  which  exists.  The  general 
term  for  these  plates  is  electrodes,  a  term  introduced  by  Faraday. 
The  air  terminals  of  the  electrodes,  to  which  the  conducting  wires 
are  attached,  are  called  the  poles.  It  should  be  noted  that  the 
copper  plate  of  the  element,  although  the  negative  electrode,  is  con- 
nected with  the  positive  pole,  and  in  like  manner  the  zinc  or  posi- 
tive electrode  is  connected  with  the  negative  pole,  because  the  current 
is  conventionally  assumed  to  flow  from  the  positive  plate,  through 
the  solution  and  out  by  the  copper  plate.  The  positive  and  negative 
poles  of  every  generator  of  electricity  are  respectively  designated  by 
the  conventional  signs  -f-  and  —  (plus  and  minus).  The  direction 
of  the  electric  current,  for  convenience  of  description,  is  conventionally 
assumed,  as  above  stated,  to  be  through  the  solutions  from  the  zinc 
to  the  copper  electrode,  and  thence  through  the  connecting  wire 
from  the  copper  to  the  zinc  electrode.  The  assumed  direction  in 
any  wire  is  denoted  by  the  conventional  sign  of  an  arrow  pointing  in 
the  direction  of  the  negative  pole. 

32.  Chemical  Reactions  Arising  in  the  Closed  Circuit. — 
The  chemical  reactions  within  the  cell,  when  its  external  circuit  is 
closed,  and  its  several  constituent  parts  traversed  by  an  electric  cur- 
rent, are  as  follows : 


Effect  of  Continued  Action.  13 

(i.)  The  oxygen  of  the  s.  z.  solution  (12)  combines  particle  by 
particle  with  the  metal  of  the  zinc  plate,  forming  oxide  of  zinc. 

(2.)  The  oxide  of  zinc,  formed  as  above,  combines  with  the  sul- 
phuric acid  of  the  s.  z.  solution  (14),  and  forms  s.  z.,  which  is  added 
to  the  s.  z.  already  present  in  the  solution  surrounding  the  zinc. 

(3.)  Oxygen  combines  with  the  s.  c.  and  forms  oxide  of  copper. 

(4.)  The  copper  in  this  oxide  separates  from  the  oxygen  and  is 
deposited  in  a  pure  metallic  form  upon  the  copper  plate. 

At  the  surface  of  the  zinc  plate,  the  oxygen  of  the  water  contained 
in  the  s.  z.  solution  is  separated  from  the  hydrogen,  while  at  the 
surface  of  the  copper  plate  this  hydrogen  combines  with  the  oxygen 
which  is  separated  from  the  oxide  of  copper. 

33.  Effect  of  Continued  Action. — This  action  goes  on  with- 
out cessation,  provided  the  circuit  remains  closed,  until  some  one  of 
the  materials  contained  in  the  cell  becomes  exhausted.      It  will  be 
observed  that  as  the  action  continues,  the  zinc  plate  is  gradually  dis- 
solved, being  oxidized,  or  in  fact  burned ;    that  the  proportion  of 
sulphate  in  the  s.  z.  solution  constantly  increases,  rendering  it  more 
dense  and  its  s.  g.  greater  ;  that,  on  the  contrary,  the  s.  c.  solution 
grows  less  dense,  and  its  s.g.  diminishes  ;  and  finally,  that  the  copper 
plate   continually  increases   in   weight,  by   the   deposition    upon   its 
surface   of  metallic  copper  abstracted  from  the   copper  solution  in 
which  it  is  immersed. 

34.  As  the  weight  of  the  s.  z.  solution,  as  indicated  by  its  s.g., 
gradually  .increases,  while  on  the  contrary  that  of  the  s.  c.  solution 
continually  becomes  less,  it  necessarily  happens  after  the  lapse  of 
a  greater  or  less  time,  the  former  becomes  heaviest,  and  consequently 
descends  to  the  bottom  of  the  cell,  forcing  the  s.  c.  solution  to  the 
top,  where   it   is  brought  into   direct  contact  with   the   zinc  plate, 
depositing   metallic   copper  thereon.     This    deposit    interrupts    the 
normal  chemical  action  of  the  cell  to  such  an  extent  that  the  electric 
current  greatly  diminishes,  and  ultimately  ceases  altogether. 

35.  By  intelligent  management  this  injurious  action  may  be  pre- 
vented, or  at  least  postponed  for  a  long  time.     The  frequent  use  of 
the  hydrometer  .(18)  is  almost   indispensable  for  this  work,  and  a 
knowledge  of  the  condition  of  the  cell  is  also  greatly  facilitated  by 
placing  it  in  front  of  a  window,  so  that  its  interior  may  be  clearly 
viewed  by  transmitted  light ;  or  at  all  events,  it  should  be  provided, 
if  possible,  with  a  white  background. 

36.  Rate  of  Consumption  of  Material. — The  rapidity  with 
which  the  materials  of  the  cell  are  consumed,  and  its  active  life  short- 
ened, depends  almost  entirely  upon  the  amount  of  work  done  by  it, 


14  Sources  of  Electricity. 

or  in  other  words,  the  quantity  of  electricity  per  unit  of  time  which 
it  is  required  to  furnish.  This  question,  which  is  an  exceedingly 
important  one,  will  be  fully  considered  further  on  (154). 

37.  Maintenance  of  the  Cell. — The  first  sign  of  the  exhaustion 
of  a  cell  generally  appears  in  the  s.  c.  solution.  It  is  not  practicable 
to  examine  the  condition  of  this  solution  by  means  of  the  hydrometer, 
but  fortunately  the  degree  of  intensity  of  its  blue  color  furnishes  an 
infallible  indication  of  its  density.  The  strong  blue  tint  of  the 
original  solution  will  after  a  time  begin  to  fade  in  the  vicinity  of  the 
upper  edge  of  the  copper  plate,  and  the  line  of  demarkation  between 
it  and  the  zinc  solution  will  become  less  and  less  distinct.  When 
this  is  seen  to  occur,  additional  s.  c.  must  be  supplied,  either  through 
the  tube  in  the  form  of  a  solution  as  directed  heretofore  (24),  or  by 
dropping  i  oz.  of  crystals  into  the  jar,  being  careful  to  observe  the 
precautions  heretofore  noted  (25).  It  is  much  better  not  to  make 
use  of  finely  powdered  s.  c.  for  this  purpose,  as  this  is  liable  to 
cement  itself  into  a  hard  insoluble  mass  at  the  bottom  of  the  cell, 
which  defies  all  efforts  to  remove  it  without  breaking  the  jar.  The 
s.  z.  solution  should  be  tested  by  means  of  the  hydrometer  (18)  at 
least  once  a  week  while  the  cell  is  in  constant  action.  The  s.  g.  of 
the  solution,  which  at  the  outset  was  about  i.io,  will  gradually  in- 
crease. When  it  reaches  1.15,  as  shown  by  the  scale,,  the  solution 
should  be  diluted  with  water.  If  the  s.  z.  solution  be  permitted  to 
approach  closely  to  its  saturation  point,  1.45,  see  table  (23),  not 
only  is  the  chemical  action  of  the  cell  diminished,  but  a  saline 
deposit  of  white  powder  (crystallized  sulphate  of  zinc)  begins  to  form 
upon  the  zinc,  and  upon  the  edge  of  the  jar  above  the  solution,  and 
by  capillary  attraction  ultimately  conveys  the  liquid  over  the  edge  to 
the  outside  of  the  cell  and  creates  a  disagreeable  nuisance.  This 
may  be  avoided  by  keeping  the  s.  g.  of  the  zinc  solution  below  1.20 
and  by  occasionally  wiping  the  inner  edges  of  the  jar  with  a  cloth  or 
sponge  saturated  with  cotton-seed  or  heavy  paraffin  oil. 

38.  Prevention  of  Evaporation. — Sometimes  a  thin  stratum 
of  one  of  the  oils  above  mentioned  is  gently  poured  upon  the  top  of 
the  zinc  solution,  after  the  cell  has  been  set  up  as  directed  in  (24), 
a  procedure  which  effectually  prevents  evaporation  and  the  formation 
of  saline  salts.  Inasmuch,  however,  as  the  presence  of  the  oil 
renders  the  cleaning  of  the  zinc  plate,  when  necessary,  a  disagree- 
able and  inconvenient  task,  it  is  perhaps  an  open  question  whether 
the  practice  is  to  be  recommended.  If  it  is  at  all  possible  to  give 
the  cell  proper  attention  from  time  to  time  as  required,  it  is  probably 
better  to  dispense  with  all  such  expedients,  but  when  such  is  not 


Prevention  of  Evaporation. 


the  case,  it  may  be  advisable  and  even   necessary  to  make  use  of 
them. 6 

39.  The  best  way  to  dilute  the  zinc  solution  is  to  use  a  tube  of 
rubber,  glass,  or  lead,  about  24  in.  long,  and  -J-  in.  diameter,  bent 
into  a  siphon,  or  an  inverted  ||,  one  leg  of  which  is  considerably 
longer  than  the  other.  Fill  the  siphon  with  water,  stopping  both 
ends  with  the  ringers,  and  after  placing  a  wooden  bucket  or  other 
convenient  receptacle  in  front  of  the  cell,  but  at  a  considerable  lower 
level,  dexterously  insert  the  tube  into  the  cell  (at  the  same  time  re- 
moving one  finger),  so  that  the  inserted  end  will  be  near  the  center 
of  the  jar  and  about  |-  in.  above  the  copper  plate,  while  the  longer 
end  is  directed  toward  the  bucket.  Now  withdraw  the  other  finsrer 

O 

from  the  lower  end  of  the  tube,  and  the  solution  will  flow  in  a  steady 

stream  into  the  bucket  so  long 

as  the  short  end  of  the  tube 

remains  immersed  (See  Fig.  8). 

Some     prefer,    instead    of    a 

siphon,  to  use  a  large  syringe, 

sold  by  dealers,  with  a  nozzle 

at  right  angles  to  the  barrel, 

having  a  capacity  of  about  3 

gills.     This  should  be   rinsed 

out  in  warm  -water  each  time 

after  it  has  been  used. 

After  withdrawing  about  I 
quart  of  the  solution  in  this 
way,  which  with  the  cell  under 
consideration  will  be  about  2 
in.  of  vertical  depth,  refill  the 
cell  to  its  original  depth,  \  in. 
from  the  top,  with  pure  soft 
water.  In  order  not  to  stir 
up  the  liquids,  this  may  with 
advantage  be  done  with  a 
small  sprinkling  pot  having  a 
fine  rose  at  the  end  of  its  spout,  or  with  due  care,  may  be  equally 
well  effected  by  holding  a  spoon  or  some  such  implement  just  at  the 
surface,  so  as  to  break  and  scatter  the  vertical  force  of  the  stream 
as  it  is  poured. 

6  Another  device  which  is  sometimes  resorted  to  for  the  purpose  of  preventing  the 
formation  of  salts  upon  the  edge  of  the  jar,  is  to  invert  the  latter  before  using,  and 
dip  it  in  a  bath  of  melted  paraffin  contained  in  a  shallow  dish,  to  the  depth  of  half  an 
inch  or  less,  which  forms,  when  cold,  an  adherent  and  repellent  coating. 


FIG.  8.     Drawing  off  Zinc  Solution. 


1 6  Sources  of  Electricity. 

40.  Dismantling  the  Cell.— The  above  described  operation,  if 
properly  carried  out,  will  practically  restore  the  cell  to  its  original  work- 
ing condition.    The  increasing  deposit  upon  the  copper  plate  will  not 
interfere  with   the  proper   action  of  the   cell,  and   need  not  be  dis- 
turbed.    The  zinc  plate,  however,  will  gradually  become   covered 
with  a  thick  coating  of  dark  brown  oxide,  which  will  adhere  to  it 
with  considerable    tenacity.     This  must  be   removed  from  time  to 
time,  especially  when,  by  becoming  of  a   reddish   color,  it  shows 
traces  of  deposited  copper.     Lift  the  zinc  plate  carefully  from  the 
solution,  and  remove  the  crust  which  has  formed  upon  the  metal,  by 
means  of  a  scraper  of  hard  wood,  or  a  stiff  brush  sold  by  dealers  in 
supplies  for  that  purpose  (a  wire  brush  answers  the  purpose  admira- 
bly).    Remove  all  the  oxide  clown  to  the  surface  of  the  metal,  wash 
the  latter  in  clean  water,  and  return  to  its  place  in  the  cell.     If  any 
undissolved  crystals  of  s.  c.  are  found  in  the  bottom  of  the  jar,  these 
should  be  washed  and  used  again. 

The  zinc  should  be  cleaned 'at  once  after  removal  from  the  cell, 
while  still  wet.  If  the  cleaning  has  to  be  deferred,  the  zinc  must  be 
placed  in  water  for  some  time  before  commencing  operations.  Great 
care  must  be  taken  to  see  that  no  water  gets  between  the  arm  of  the 
zinc  and  the  brass  binding-screw,  as  this  will  cause  a  deposit  of  sul- 
phate of  zinc,  which  may  entirely  prevent  the  passage  of  the  current 
when  the  zinc  is  again  put  to  use. 

41.  Diffusion  of  Solution  within  the  Cell. — An  absolute 
separation  of  the  copper  and  zinc  solutions  in  the  voltaic  cell  cannot 
be  attained.     Liquids  of  unlike  density  separated  from  each  other 
by  gravity  always  tend  to  intermingle  by  a  slow  process  of  diffusion, 
and  thus  ultimately  to  form  one  homogeneous  solution.     This  ten- 
dency may  be  reduced  to  a  minimum  by  intelligent  management  and 
proper  attention  to  the  requirements  of  the  cell  while  in  action,  so  as 
to  cause  but  little  practical  inconvenience. 

42.  The  solutions  manifest  a  much  stronger  tendency  to  mix  when 
the  cell  is  on  open  than  when  on  closed  circuit.     Hence,  cells  in 
which  the  solutions  are  separated  by  gravity,  and  in  fact  all  sulphate 
of  copper  cells,  give  the  most  satisfactory  results  when  used,  as  in 
telegraphy,  upon  circuits  which  are  closed  the  greater  portion  of  the 
time. 

43-  Neutralizing  the  Zinc  Solution. — When  the  cell  is  dis- 
mounted and  renewed,  the  s.  z.  should  be  drawn  off  with  the  siphon 
and  thrown  into  a  wooden  vessel,  together  with  a  few  pieces  of 
metallic  zinc,  which  will  purify  the  liquid  by  reducing  any  metallic 
copper  which  may  be  present  in  it.  It  should  then  be  filtered  or 


Waste  Products  of  the  Cell.  1 7 

strained  through  cloth  or  sand,  and  afterward  diluted  with  water 
until  its  specific  gravity  is  reduced  to  i.io.  It  is  then  in  suitable 
condition  to  be  used  in  the  renewed  cell,  instead  of  making  a  new 
solution  as  directed  in  (20). 

44.  Waste  Products  of  the  Cell.— Where  a  large  number  of 
cells  are  in  constant  use,  it  is  generally  worth  while  to  dry  and  pre- 
serve the  material   thus  removed   from  the  zincs,  commonly  called 
"battery  mud,"  as  it  is  rich  in  metallic  zinc  and  copper,  and  will 
usually    be    willingly  purchased    at   a   fair   price  by   brass-founders. 
When  the  copper  plates  have  become  heavily  encrusted  with  metallic 
deposits,  they  may  with  advantage  be  disposed  of  in  the  same  way. 
Electrotype  or  deposited  copper,  as  this  is  termed,  is  much  valued 
in  many  of  the  industrial  arts. 

45.  Copper  plates  which  have  been  used  in  the  battery,  and  which 
are  intended  to  be  used  again,  should  be  kept  in  water;  taking  care 
that  the  connecting  wire,  with  its  coating  of  gutta-percha  or  india- 
rubber,  is  completely  immersed.     Zinc  plates,  on  the  contrary,  must 
be  kept  in  a  dry  place,  never  in  water. 

46.  Other  Forms  of  the  Cell. — Much  unprofitable  ingenuity 
has  been  displayed  by  inventors  in  varying  the  form,  proportions  and 
relations  of  the  elements  of  the  sulphate-of-copper  cell,  in  pursuit  of 
imaginary  advantages.      As  a  matter  of  fact,  it  has  been  found  to  be 
almost  wholly  immaterial   what   the    form   and   arrangement  of  the 
parts  may  be,  so  long  as  the  necessary  general  principles  of  action 
are  kept  in  view.      The  consumption  of  a  given  amount  of  zinc  and  sul- 
phate of  copper  can  never  in  any  chemical  combination,  or  under  any 
circumstances,  evolve  more  than  a  definite  and  perfectly  well  ascertained 
quantity  of  electricity,  in  a  form  available  for  use,  although  if  the  cell 
be  unskillfully  proportioned  or  arranged,  the  quantity  of  electricity 
evolved  may  be  less  than  it  should  be  (154).     The  principal  differ- 
ence between  different  forms  is  that  some  require  less  frequent  atten- 
tion  than  others  ;  but  this  advantage    is  sometimes    gained  at  the 
expense  of  other  more  valuable  qualities. 

47.  Among  the  different  practical  voltaic  cells  which  have  been 
employed  in  America  to  a  greater  or  less  extent,  commonly  known 
by   the    names    of  their   originators    and    designers,  but   involving 
essentially   the    same    principles    as  the  one   which    has   been    de- 
scribed,  may  be  mentioned  the  Hill,7  Callaud,8   Minotto,9   Thom- 

7  L.  BRADLEY  in  The  Telegrapher,  iii.  153 ;  E.  A.  HILL  in  the  same,  iii.  201. 

8  BLAVIER  :  Telegraphie  Electrtque,  i.  271 ;   POPE  :  Modern  Practice  of  the  Electric 
Telegraph  (4th  ed.),  106. 

»  F.  JENKIN  :  Electricity  and  Magnetism,  225. 


1 8  Sources  of  Electricity. 

son,10  etc.,  etc.,  for  a  particular  description  of  which  recourse  may 
be  had  to  the  publications  indicated  in  the  references. 

48.  The  Lockwood  Cell.— This  form  of  cell  has  been  found 
to  give  excellent  results  in  cases  in  which  a  moderate  but  perfectly 
uniform  current  is  required  without  attention  for  a  great  length  of 
time.  The  jar  is  of  extra  depth  (9  in.)  and  the  copper  plate  consists 
of  two  flat  spirals  of  wire  coiled  like  a  clock-bell  and  laid  in  reverse 
directions  to  each  other,  one  beneath  and  the  other  at  the  top  of  a 
mass  of  5  Ibs.  of  s.  c.  in  crystals,  placed  in  the  bottom  of  the  jar. 
The  connecting  wire  is  continuous  with  the  lower  spiral,  while  the 
two  spirals  are  united  by  a  vertical  rod  or  stout  wire  which  is  con- 
nected to  their  inner  ends.  The  action  of  the  current  traversing  the 
coils  appears  to  act,  in  some  manner  not  well  ascertained,  to  oppose 
the  tendency  of  the  s.  c.  solution  to  ascend  in  the  jar  and  reach  the 
zinc  plate.  A  series  of  these  cells  will  maintain  a  current  for  a 
year  under  favorable  conditions. 

49-  The  Daniell  Cell.— This  is  the  original  form  of  the  sul- 
phate of  copper  element.  It  was  formerly  much  used  in  the  tele- 
graphic service,  but  has  now  been  practically  superseded  by  the 
equally  efficient  and  more  economical  gravity  cell.  As  usually  con- 
structed, the  Daniell  cell  consists  of  a  jar  of  glass  or  earthenware  F 
(Fig.  9)  6  in.  in  diameter  and  8  in.  high.  A  thin  sheet  of  copper  G 
is  bent  into  a  cylindrical  form  so  as  to  fit  loosely  within  the  jar,  and 
to  this  is  affixed  a  chamber  provided  with  a  perforated  bottom, 
designed  to  receive  a  supply  of  s.  c.  in  crystals.  A  copper  strip  is 
riveted  to  the  plate  G  and  provided  with  a  clamp  at  its  extremity, 
adapted  either  to  receive  a  conducting  wire,  or  to  connect  to  the  zinc 
plate  of  the  next  adjacent  element,  as  the  case  may  be.  Within  the 
copper  cylinder  is  a  porous-cup  (as  it  is  technically  termed),  H,  of 
unglazed  porcelain  ware,  7  in.  high  and  2  in.  diameter,  within  which 
is  placed  a  bar  of  cast  zinc  of  the  cross-section  shown  at  X,  or  as 
sometimes  preferred,  a  hollow  cylinder  with  a  vertical  slit  in  one 
side,  the  latter  form  yielding  a  somewhat  greater  quantity  of  elec- 
tricity, but  being  less  convenient  to  clean. 

50.  The  porous-cup  H  is  filled  with  s.  z.  solution  prepared  as 
directed  in  (20)  and  the  jar  outside  the  porous-cup  with  s.  c.  solution 
of  s.  g.  1. 10.  A  quantity  of  the  crystals  may  be  placed  in  the  per- 
forated chamber  attached  to  the  copper  plate,  which  gradually  dis- 
solve and  thus  maintain  the  solution  at  its  proper  density.  Pure 
water  may  be  used  in  the  porous  cell  as  directed  in  (21)  if  pre- 
ferred. 

10  F.  JENKIN  :  Electricity  and  Magnetism,  223. 


Maintenance  of  the  Daniell  Cell. 


51.  Maintenance  of  the  Daniell  Cell. — This  cell  is  main- 
tained in  substantially  the  same  manner  as  the  gravity.  Unless  a 
very  large  volume  of  current  is  required,  it  will  be  found  much  more 


FIG.  9.    The  Daniell  Cell. 

economical  to  feed  the  s.  c.  solution  with  small  quantities  of  crystals, 
placed  in  the  chamber  once  in  every  two  or  three  days,  and  keeping 
the  solution  but  half  saturated  (s.  g.  i.io)  and  uniform  in  color 
throughout,  by  stirring  it  with  a  wooden  or  glass  rod.  The  s.  z. 
solution  should  be  maintained  as  nearly  as  possible  at  the  same  s.  g. 
as  the  copper  solution. 

52.  Renewal  of  the  Daniell  Cell.— When  taken  apart  for 
cleaning,  more  or  less  copper  will  usually  be  found  deposited  in 
patches  on  the  porous-cup.  This  deposit  cannot  be  prevented,  but 
may  be  greatly  diminished  by  suspending  the  zinc  free  from  the  bot- 
tom or  sides  of  the  porous-cup,  or  even  by  placing  a  piece  of  glass  in 
the  bottom  of  the  cup  for  the  zinc  to  stand  on.  It  is  also  a  good 
plan,  for  the  same  reason,  to  saturate  the  bottom  of  the  porous-cup 
to  the  height  of  half  an  inch  with  melted  paraffin  or  tallow  before 
putting  it  to  use.  The  porous-cup  ought  to  be  replaced  by  a  new 


2O  Sources  of  Electricity. 

one  whenever  as  much  as  half  of  its  surface  has  become  encrusted 
with  metallic  copper  by  continued  use.  If  it  becomes  cracked  it 
should  be  replaced  at  once,  or  a  great  waste  of  material  will  ensue. 

The  porous-cup  of  an  element  intended  only  for  occasional  use, 
may  with  advantage  be  made  thicker  and  less  porous  in  texture  than 
if  intended  to  be  kept  continuously  in  action. 

53.  Intermingling  of  the  Solutions.— It  should  be  observed 
that  at  the  best,  a  porous  cell  merely  obstructs  and  does  not  prevent 
the  ultimate  intermingling  of  the  copper   and  zinc  solutions.     The 
liquids  will  pass  through  the  porous  wall  of  the  cup  by  virtue  of  a 
singular  property,  common  to  all  dissimilar  liquids  when  separated 
by  a  porous   partition,11   and   will   be   found    to  exhibit  a  constant 
tendency  to  rise  in  the  outer  cell  and  to  disappear  from  the  porous- 
cup.     This   tendency  is  obviously  assisted  by  the  passage  of  the 
current. 

54.  Porous-cups   which   have   been   used   in    a  cell,  must   not  be 
allowed  to  become  dry  after  being  taken  out,  but  should  be  kept  in 
water,  otherwise  the  crystallization  of  the  s.  z.  contained  in  the  pores 
will  almost  certainly  break  them. 

55.  Choice  of  Battery  Materials. — The  s.  c.  and  the  metallic 
zinc  used  for  electrical  purposes  should  be  of  good  quality  and  free 
from  adulterations.     Adulterated  s.  c.  is  very  seldom  met  with  in  the 
United  States  ;  that  sold  by  dealers  in  electrical  supplies  is  almost 
uniformly  of  good  quality.     The  best  commercial  zinc  usually  con- 
tains a  small  proportion  of  iron  and  lead.     An  analysis  of  spelter  of 
good  quality  for  electrical  purposes,  gave  : 

Zinc 98.76  per  cent. 

Lead 1.18 

Iron 0.06 

56.  The  question  of  the  effects  of  temperature  upon  the  efficiency 
of  the  voltaic  cell  is  a  very  important  one,  and  merits  much  more 
consideration  than  it  has  hitherto  received.     The  sulphate  of  copper 
cell  is  especially  sensitive  in  this  particular,  and  should  be  carefully 
guarded  against  cold.     This  subject  is  further  considered  in  a  subse- 
quent chapter  (162). 

57-  General  Directions  for  the  Care  of  Cells.— The  direc- 
tions for  the  management  of  the  sulphate  of  copper  element  may  be 
summarized  as  follows  : 

(i.)  Place  the  cells  in  a  clean,  dry,  and  well  lighted  situation,  not 
exposed  to  dust  nor  to  extremes  of  temperature. 

"JOHNSON'S  Univ.  Cyclopedia,  Art.  Endosmose. 


The  Oxide  of  Copper  Cell. 


21 


(2.)  Do  not  move,  shake,  or  stir  the  cells  after  the  s.  c.  solution 
has  been  introduced  into  them. 

(3.)  Start  each  cell  with  s.  z.  solution  at  s.g.  i.io  (or  15°  Baume), 
and  s.  c.  solution  not  below  s.g.  1.20  (or  25°  Baume). 

(4.)  Keep  the  s.  c,  solution  of  a  strong  blue  color  up  to  a  point 
just  above  the  copper  plate,  by  adding  s.  c.  as  fast  as  it  is  consumed 
by  the  action  of  the  current,  but  be  careful  never  to  put  in  too  much 
s.  c.  at  one  time. 

(5.)  Test  the  s.z.  solution  frequently  with  the  hydrometer,  and 
when  its  s.g.  reaches  1.15  (or  20°  Baume),  dilute  with  water  to  re- 
duce it  to  i.io  (15°  Baume). 

(6.)  Wipe  off  with  a  greasy  cloth  any  crystallized  s.  z.  which  forms 
upon  the  edges  of  the  jars. 

(7.)  Do  not  let  the  zinc  become  too  heavily  coated  with  brown 
oxides.  If  the  oxides  tend  to  form  into  pendants,  hanging  below  the 
zinc,  detach  these  at  once  with  a  bent  wire  ;  they  cause  a  great  waste 
of  material. 

(8.)  It  is  an  excellent  plan  to  wrap  the  zinc  neatly  in  linen  paper 
(the  kind  called  parchment  paper  is  best),  securing  the  folded  flaps 
at  the  top  with  sealing-wax,  and  tying  strongly  with  twine  passed 
several  times  around  the  whole.  This  expedient  prevents  particles 
of  zinc  from  falling  on  the  copper,  and 
also  aids  the  action  of  gravity  in  pre- 
venting the  too  rapid  upward  diffusion 
of  the  s.  c.  solution. 

58.  The  Oxide  of  Copper  Cell. 
—A  voltaic  combination  in  which  the 
metallic  elements  are  amalgamated 
zinc 12  and  protoxide  of  copper  (Cu  O),13 
and  the  exciting  agent  a  solution  of 
caustic  potash  ( K  O ),  has  of  late 
found  much  favor  in  the  telegraphic 
service,  under  the  name  of  the  Edi- 
son-Lalande  cell.  In  the  size  designed 
for  this  use,  the  glass  contain  ing-jar  is 
8  in.  high,  6  in.  in  diameter,  and 


FIG.  10.     Oxide  Plate  of  Edison- 
Lalande  Cell. 


12  Zinc  which  has  been  immersed  in  dilute  sulphuric  acid,  and  then  coated  with 
mercury,  is  said  to  be  amalgamated.     This  process  renders  the  chemical  action  upon 
the  zinc  more  uniform  and  less  wasteful  in  certain  forms  of  voltaic  elements.     It  is  of 
no  advantage  in  the  sulphate  of  copper  element. 

13  Protoxide  of  copper  is  obtained  by  roasting  copper  turnings.     The  product  is  then 
ground  to  powder  and  compressed  into  solid  masses,  from  which  are  cut  plates  of 
suitable  size  for  the  cell. 


22 


Sources  of  Electricity. 


weighs  5.75  Ibs.  It  is  provided  with  a  porcelain  cover,  from  which 
are  suspended  two  rectangular  plates  of  rolled  zinc,  fitted  with  a 
double  clamp-screw  for  attaching  the  wire.  A  skeleton  frame  of 

copper  (Fig.  10)  is  fitted  to  clasp 
two  rectangular  slabs  containing  i 
Ib.  of  copper  oxide,  and  is  suspend- 
ed from  the  porcelain  cover  be- 
tween and  facing  the  zinc  plates. 
To  prevent  possible  contact,  a  fen- 
der of  hard  rubber  is  inserted  be- 
tween the  oxide  plates,  projecting 
on  each  side.  A  transverse  cop- 
per bolt  and  nut  clamps  the  whole 
firmly  together.  Fig.  n  shows 
the  appearance  of  the  cell  when 
mounted. 

59.  Setting  Up  and  Main- 
taining the  Oxide  of  Copper 
Cell. — The  solution  for  this  cell 
consists  of  i  part  by  weight  of  caus- 
tic potash  dissolved  in  3  parts  pure 
soft  water  (s.  g.  1.33 ;  38°  Baume), 

with  which  the  jar  is  to  be  filled  to  within  i  in.  of  the  top.  Caustic 
potash,  in  sticks  of  a  size  just  sufficient  to  make  the  proper  solution, 
are  usually  supplied  by  dealers.  The  solution  should  be  stirred  with 
a  wooden  or  glass  rod  while  the  potash  is  dissolving,  otherwise  the 
evolution  of  heat  may  fracture  the  jar.  Finally,  a  stratum  of  heavy 
paraffin  oil  (s.  g.  1.46  ;  48°  Baume),  about  J  in.  deep,  is  poured  upon 
the  solution  to  prevent  evaporation. 

The  cell  will  ordinarily  require  no  further  attention  until  its  mate- 
rials are  entirely  consumed,  when  both  the  zinc  and  oxide  plates,  as 
well  as  the  solution,  must  be  renewed. 

60.  Chemical  Reactions  of  the  Oxide  of  Copper  Cell.— 
When  the  external  circuit  is  closed,  the  oxygen  of  the  water  in  the 
solution,  uniting  with  the  zinc,  forms  oxide  of  zinc  as  in  other  cells. 
This,  combining  with  the  potash  in  the  solution,  forms  a  soluble 
double  salt  of  zincate  of  potash,  which  is  decomposed  as  rapidly  as 
it  is  formed.  The  hydrogen  which  is  set  free  unites  with  the  oxygen 
of  the  protoxide  of  copper  of  the  negative  plate,  and  deposits  metallic 
copper.  The  reaction  takes  up  i  equivalent  of  zinc,  i  of  potash,  i 
of  protoxide  of  copper,  and  deposits  i  equivalent  of  metallic  copper. 
The  wasteful  local  action  in  this  cell  is  so  small  as  to  be  practically 


FIG.  ii.    Edison-Lalande  Cell. 


The  Grove  and  Bunsen  Cells. 


FIG.  \\a. 
d'Infreville's  Wasteless  Zinc 


negligible,  which  is  an  important   advantage.14     The   copper  is  de- 

posited in  a,  pure  form,  suitable  for  industrial  uses. 

61.   The  Grove  and  Bunsen  Cells.  —  Other  voltaic  combina- 

tions, formerly  largely  used  in  telegraphy  but  now  obsolete,  consist 

of  amalgamated  zinc  in  dilute  sulphuric  acid,  and  platinum  in  nitric 

acid  known  as  the  Grove,  and  carbon  in  bichromate  of  potash  solu- 

tion known  as  the  Bunsen.15 

6ia.  The  Wasteless  Battery  Zinc.  —  The  unavoidable  waste 

of  metal  in  the  gravity  cell  (10)  from  the  unconsumed  part  of  each 

zinc  electrode  which  has  to  be  thrown  aside,  sometimes  amounts  to 
45  per  cent,  of  the  original  weight.  This 
loss  is  avoided  by  the  "  wasteless  "  electrode 
invented  by  G.  dTnfreville,  which  is  made 
up  of  two  or  more  similar  sections^  each 
formed  of  a  hub  with  inclined  radial  arms 
(see  Fig.  n#.)  The  hubs  of  the  several  sec- 
tions are  slightly  coned,  and  fit  snugly  into 
one  another.  Fig.  \\b.  shows  an  electrode 
of  three  sections  after  having  been  some  time 

in  use.     When  the   lowermost  section  has 

been  nearly  consumed,  a  new  one  is  added 

at  the  top,  and  in  this  way  each  is  oxidized 

in  turn  without  waste.     The  coned  form  of 

the  hubs  enables  the  sections  to  be  put  to- 

gether in  a  perfectly  secure  manner  by  a 

light  blow.     With  this  electrode,  the  resist- 

ance (153)  per  Cell  is  reduced    tO    One-third      Sectional  view  of  Wasteless  Zinc. 

its  former  value,  while  much  is  gained  in  constancy. 

A  brass  hanger  or  support  accompanies  the  zinc,  which  grasps  it 
securely  by  an  ingenious  elastic  friction.  A  plan  view  of  this  hanger 

is  shown  in  Fig.  nc.  A  con- 
necting wire  of  any  thickness 
may  also  be  firmly  clamped,  as 

FIG.  1I,.-d'infreviiie-5  Hanger.  shown,  between  the  branches  of 

the  Y-shaped   extremity  of  the  hanger,  the  arms  of  which  interlock 
by  their  own  elasticity  so  as  to  hold  it  securely. 

14  F.  DELALANDE  and  G.  CHAPERON  in  L  Electricien,  vi.  98,  103  ;  Electrical  Review 
^London),  xiii.  59,  102;  xiv.  485;  N.  Y.  Electrical  Engineer,  ix.  153. 

1  *  For  description  and  directions  for  management  of  the  Grove  cell  see  Modem  Practice 
vfthe  Electric  Telegraph,  4th  ed  ,  15  ;  and  for  Bunsen  bichromate  cell,  the  same,  p  17. 


FIG.  \\b. 


OF  THK 

UNIVERSITY 


CHAPTER   III 

THE    SOURCES   OF    ELECTRICITY.— (Continued.) 

62.  Magneto-Electricity. — Electricity  which  is  evolved  from 
a  magnet,  by  moving  coils  of  wire  within  the  sphere  of  its  influence 
by  mechanical  power,  is  called  magneto  or  dynamo-electricity.     The 
distinction  between  the  two  is  purely  arbitrary  and  nominal,  and  has 
reference  only  to   the   particular   structure  and  organization  of  the 
machines  from  which  they  are  respectively  derived. 

63.  Magnetism. — It  has  been  known  from  time  immemorial  that 
certain  natural  ores  of  iron  possessed  the  property  of  attracting  iron 
and  steel,   and  that  these    metals   were    themselves   capable,  under 
proper  conditions,  of  being   endowed  with  a  like   property.     This 
property,  which  is  called  magnetism,  is  also  capable  of  being  mani- 
fested, though   in   a  less    marked  degree,  by  certain  other  metals, 
especially  cobalt  and  nickel.     Such  a  mass  of  magnetic  ore  is  called  a 
natural    magnet    or   lodestone.     A   mass    of  iron   or   steel   to  which 
magnetic  properties  have  been  imparted  by  any  known  means,  is 
called  an  artificial  magnet.     Soft  iron  is  capable  of  retaining  magnetic 
properties   only   during   such  time   as   it   remains   under  the  direct 
influence  of  the  magnetizing  force,  and  under  such  conditions  is  said 
to  be  a  temporary  magnet.      Hardened  iron    or  steel   continues  to 
retain  magnetic  properties  after  the  withdrawal  of  the  magnetizing 
force ;  and  hence  a  mass  of  hardened   steel,  when  magnetized,  is 
called  a  permanent  magnet.1 

64.  The  Magnetic  Needle. — A  piece  of  hardened  steel,  which 
has  been  permanently  magnetized,  possesses  marked  peculiarities. 
When  a  straight  bar  of  this  kind,  which  is  termed  a  bar-magnet,  is 
suspended  freely  by  its  center  of  gravity,  it  always  tends  to  place 
itself  approximately  north  and  south,  usually  in  the  direction  of  its 
greatest  length.     The  imaginary  line  in  which  it  thus  places  itself 
is  termed  the  magnetic  meridian.     A  small  magnetic  steel  bar,  when 

1  For  an  exposition  of  the  modern  theories  of  magnetism,  the  student  is  referred  to 
the  papers  of  D.  E.  Hughes,  Proc.  Royal  Soc.,  1879,  p.  56;  J.  A.  Ewing,  Royal  Soc., 
1890;  Elec.  World,  xvi.  241.  A  summary  will  be  found  in  Kapp,  Electric  Trans- 
mission of  Energy,  16.  The  celebrated  lecture  of  Prof.  A.  M.  Mayer,  The  Earth  a 
Great  Magnet,  New  Haven,  1872,  presents  the  whole  subject  of  magnetism  in  a  most 
admirable,  popular  way. 

24        • 


Phenomena  of  Magnetic  Induction. 


suspended  by  a  filament,  as  shown  in  Fig.  12,  or  upon   a  pivot,  as 
shown  in  Fig.  13,  is  called  a  magnetic  needle.     Such  a  needle,  in  con- 
junction with  a  graduated  dial,  consti- 
tutes the  well-known  magnetic  compass. 
65.    Phenomena    of   Magnetic 
Induction. — When  an  artificial  mag- 
net is  placed  in  the  immediate  neigh- 
borhood of  one  or  more  pieces  of  iron, 
or  of  a  quantity  of  iron  chips  or  filings, 
these    are    instantly   at- 
tracted.      They     attach 

themselves  to  the  magnet,  and  will  be  found  to  adhere 
with  considerable  force  to  its  surface.      At  the  same 
time,  a  magnetic  influence  is  exerted  upon  these  bod- 
ies by  virtue  of  which  they  themselves  become  mag- 
nets.     The  magnetism  thus  appearing  in  such  bodies 
is  said  to  be  induced  \\\  them,  and  this  process  of  im- 
parting or  developing  magnetism  is  called 
magnetic  induction.    Thus,  in  Fig.  14,  NS 
is  a  bar-magnet,  k  is  an  iron  key  which 
is    attracted   and   held    suspended    by  it, 
and  ;/  is  an  iron  nail,  in  turn   held   in  the 
same   way   by  the  key,   which   has   itself  become   a   magnet.      The 

original   magnetizing  body  suffers  no 

loss  of  magnetism  by  this  process. 
66.  Polarity  of  the  Magnet.— 

If  a  bar-magnet  be  rolled  in  a  mass 

of  filings  or  other  small  fragments  of 

iron,  these  will 

be     found     to 

assemble        in 

much     irreater 


FIG.  13,     Magnetic  Needle  on  Pivot. 


Fm. 


Suspended  Magnetic 
Needle. 


FIG.  14.     Attraction  of  Magnet. 


quantity  near  each  of  the  ends  than  toward  the  middle  of 
the  bar,  as  shown  in  Fig.  15.  This  shows  that  the  attractive 
force  of  a  magnet  is  at  its  maximum  at  two  points  situated 
near  the  respective  ends  of  the  bar,  and  gradually  diminishes  toward 
the  center,  where  it  disappears  altogether.  These  two  points  of 
maximum  attraction  are  termed  the  poles  of  the  magnet.  The  one 


26 


Sources  of  Electricity. 


'    •     •'••     '      '          !     ':      '      ''!'.,       •'•'.•.    i:       ;-;"''•     !i  ": 


FIG.  15,     Attraction  of  Iron  Filings  by  Bar- Magnet. 


which  points  toward  the     north  pole  of  the  earth  when  the  magnet 
is  suspended,  is  conventionally  termed  the  boreal  or  north  pole  (71), 

and  the  opposite  one 
the  austral  or  south 
pole* 

The     intermediate 
point,    where    no    at- 
traction   is    manifest- 
ed,, is  called  the  neu- 
tral line  or  equator  of  the  magnet.      Some  magnets,  termed  multi- 
polar  magnets,  have  more  than  one  set  of  poles. 

The  distance  between  the  poles  of  a  magnet  is  called  its  magnetic 
length.  In  most  bar-magnets  it  is  about  0.83  of  the  total  length.  In 
a  horseshoe  magnet  (67)  it  is  the  shortest  distance  between  the  poles. 
A  magnet  need  not  necessarily  be  magnetized  in  the  direction  of 
its  greatest  length  ;  a  bar  may  be  magnetized  transversely,  or  in  fact 
in  any  direction.  When  a  magnet  is  broken  into  detached  parts, 
each  fragment  instantly  becomes  an  independent 
magnet,  having  a  north  and  south  pole. 

67.  Horseshoe      Magnet     and     Arma- 
ture1.— Instead  of  being  straight,   as  in  Fig.  14, 
it    is  more    usual,    as    well    as    more    convenient, 
for    the    magnetic   bar   to    be    given    a    form    re- 
sembling   the    letter    U»    as    m    Fig.    16.       This 
form  is  known   as   the  horseshoe  magnet.     A   soft 
iron    armature  is    usually  fitted   to   the  poles    of 
a  horseshoe  magnet.      This  is  sometimes  called 
the  keeper,  because  it  aids  in  retaining  or  keeping 
the    magnetic   qualities    of  the    bar.      In   general 
terms,  any  mass  of  iron  or  steel  subjected  to  the 
attraction   of  a    magnet    is    considered    to   be   an 
armature. 

A  magnetic  attraction  has  been  experimentally 
produced  between  a  magnet  and  its  armature  as 
high  as  i. ooo  Ibs.  per  sq.  in.  of  surface  in  con- 
tact.3 

68.  The  Magnetic  Spectrum. — If  a  sheet  of  thin  glass  or 

2  The  north  pole  of  a  magnetic  bar  or  needle,  by  convention,  is  usually  painted  blue> 
and  the  south  pole  red.     Sometimes  they  are  respectively  stamped  with  the  letters  N 
and  S,  and  sometimes  a  straight  line  or  mark  serves  to  designate  the  north  pole. 

3  EWING  and  Low  :  Phil.   Trans.   Royal  Soc.,   1889,  A.  221  ;  see  also  H.  E.  J.  G- 
Du  Bois  :   Phil.  Mag.,  April,  1890. 


FIG.  16.     Horseshoe 
Magnet  and  Arma- 
ture. 


The  Magnetic  Field. 


27 


card-board  be  laid  upon  a 
bar-magnet,  and  its  surface 
sprinkled  with  iron  filings 
from  a  pepper-box,  as  in 
Fig.  17,  upon  tapping  the 
sheet  with  a  pencil  or  simi- 
lar object,  a  remarkable 
phenomenon  will  occur. 
The  particles  of  iron  will 
arrange  themselves  sym- 
metrically in  curiously  FIG.  17 
curved  lines  as  shown  in 
Fig.  1 8,  which  is  taken  from  a 


FIG.  18.    Spectrum  of  Bar-Magnet. 


.     Method  of  producing  Magnetic  Spectrum. 

photograph.     This  is  called   the 
magnetic  spectrum. 

69.  The  Mag- 
netic Field.— The 
sphere  of  attraction 
which  surrounds  a 
magnet  is  termed  the 
magnetic  field,  and  is 
filled  with  what  were 
happily  termed  b\ 
Faraday,  lines  of  mag- 
netic force.  These 
exist  unseen  in  every 
magnetic  field,  but 
their  presence  and 
direction  may  be 
made  evident  by  the 
expedient  which  has 
just  been  described. 
Magnetic  force  in  it- 
self is  absolutely  in- 
We  only  know  of  its  existence 


appreciable  by  any  of  our  senses 
by  its  effects  upon  matter. 

Since  the  peculiarities  of  the  magnetic  field  are  due  to  the  presence 
of  a  force,  the  properties  of  such  a  field  may  be  made  known  by 
determining  the  strength  and  the  direction  of  this  force,  or,  as  it  is 
usually  expressed,  the  intensity  of  the  field,  and  the  direction  of  the 
lines  of  force* 

« Force  is  any  action  which  can  be  expressed  simply  by  weight,  and  is  distinguished 
by  a  great  variety  of  terms,  such  as  attraction,  repulsion,  gravity,  pressure,  tension, 


28 


Sources  of  Electricity. 


FIG.  19.     Lines  of  Force  of  liar- Magnet. 


70.  Lines  of  Magnetic  Force. — The  invisible  lines  of  mag 
netic  force  radiate  in  every  direction  from  each  pole  of  the  magnet. 
They  may  be  regarded  as  an  inseparable  part  of  it,  which  accompany 
it  wherever  it  goes.     Perhaps  their  true  nature  may  be  more  clearly 

conceived  by  assuming  them  to  set 
out  from  one  pole,  say  the  north 
pole,  and  after  curving  for  a 
greater  or  less  distance  through 
space,  to  return  again  to  the  south 
pole,  as  indicated  by  the  arrows 
in  Fig.  19.  A  view  of  the  spec- 
trum of  the  magnetic  field  at  one 
pole  of  a  bar-magnet,  as  seen 
end-on,  exhibits  merely  radial  lines,  as  in  Fig.  20. 

71.  If  a  small  bar- 
magnet    or  magnetic 
needle  be  suspended 
at    any    point   within 
the   field  of  a  larger 
magnet,  it  will  invari- 
ably tend  to  place  it- 
self parallel     to    the 
line    of    force    which 
passes    through  both 
its  poles,  as  shown  in 
Fig.    21.       This    exT 
plains  why  the  needle 
of  the  magnetic  com- 
pass always  points  to 
the  north.     The  earth 
itself  is  a  great  mag- 
net, and  is  surrounded 
by  a  field  filled  with 

invisible  lines  of  force  which  we  term  magnetic  meridians.  These 
lines  determine  the  position  of  the  suspended  magnetic  needle. 
Thus  by  exploring  with  such  a  needle,  the  direction  of  the  lines  of 
force  in  any  magnetic  field  may  be  discovered  (94). 

72.  Attraction  and  Repulsion. — The  respective  north  poles 

compression,  cohesion,  adhesion,  resistance,  inertia,  strain,  stress,  strength,  thrust, 
load,  squeeze,  pull,  push,  etc.,  all  of  which  can  be  measured  or  expressed  by  weight, 
without  regard  to  motion,  time,  power  or  work.— J.  W.  NYSTROM  :  Elements  of 
Mechanics,  p.  59. 


FIG.  20.    Spectrum  of  Magnet  Pole — End-on. 


Current  Produced  by  a  Magnetic  Field.         29 


of  any  two  magnets  repel  each  other,  and  so  do  the  south  poles  ;  but, 
on  the  contrary,  the  north  and  the  south  pole  of  the  same  or  differ- 


FIG.  21.     Position  of  Magnetic  Needle  in  Field.— J.  A. 


ent  magnets  mutually  attract  each  other.  Hence  it  follows  that  the 
north  pole  of  any  magnet  must  have  the  same  polarity  as  the  south 
pole  of  the  earth,  and  in  strictness  ought  to  be  termed  the  south 
pole  rather  than  the  north  (66).  It  is  more  properly  termed  the 
north-seeking  pole. 

73.  Electric  Current 
Produced  by  a  Mag- 
netic Field. — If  a  con- 
ducting wire  in  the  form 
of  a  closed  loop  or  end- 
less ring  be  moved  within 
a  magnetic  field,  in  any  di- 
rection whatsoever  which 
alters  the  number  of  lines 
of  force  passing  through 
it,  a  current  of  electricity  will  appear  in  the  wire.  The  same  thing 
will  occur  if  the  wire  be  stationary  and  the  field  be  moved ;  or  if 
the  wire  be  stationary  and  the  intensity  or  strength  of  the  field  be 
increased  or  diminished,  either  between  zero  and  maximum,  or  to 
a  lesser  extent ;  or  if  the  wire  be  moved  from  one  part  of  the  field 
to  another  part  of  different  intensity.5 

»  FARADAY'S  own  account  of  this  capital  discovery  of  magneto-electricity— the  results 
of  which  are  likely  to  ultimately  become  of  greater  importance  than  any  other  ever 


,  —  •>. 

,  v 

(/~\\ 

/ 

I     \ 

\1         _J 

\\ 

1 

'      1 

/ 

/ 

T 

v  / 

/ 

\  // 

\^ 

^^/ 

^-  

FIG,  22.    Lines  of  Force  not  cut  by  Movement  of  Ring. 


Sources  of  Electricity. 


74-  Thus  in  Fig.  22,6  let  the  parallel  arrows  be  assumed  to  repre- 
sent lines  of  'force  in  a  uniform  magnetic  field.  If  the  closed  ring 
of  wire  be  moved  parallel  to  those  lines,  as  indicated  by  the  dotted 

arrow,  no  electric  current 
will  appear  in  the  ring. 
Or  if  the  ring  and  the 
lines  of  force,  either  or 
both,  be  moved  in  a  trans- 
verse direction  with  ref- 
erence to  each  other,  with- 
out altering  the  total  num- 
ber of  lines  enclosed,  as 
shown  in  Fig.  23,  no  cur- 
rent will  be  generated  in 


FIG.  33.    Movement  of  Translation  in  Uniform  Field. 


\V7 


the  ring.  Fig.  24,  on  the 
other  hand,  represents  a 
field  which  is  not  uniform,  being  stronger  or  more  intense,  or  in 
other  words,  having  a  greater  number  of  lines  of  force,  in  some  parts 
than  in  others.  Moreover,  as  shown  by  the  arrow-heads,  these  lines 

run  in  opposite  directions  in      ^ 

different  parts  of  the  field. 
If,  now,  the  ring  be  moved 
from  a  place  where  the 
lines  of  force  are  more 
numerous  to  a  place  where 
they  are  less  numerous,  as 
from  position  i  to  position 
2  in  Fig.  24,  a  current  will 
be  generated  -}  and  if  this 
motion  be  continued,  as  in 
position  3,  to  a  place  where 
the  lines  run  in  an  opposite 
direction,  the  effect  will  be 
similar  in  kind,  but  will  be 
even  greater  in  amount.  So,  also,  if  the  ring  be  moved  in  a  uniform 
field  in  such  a  manner  that  either  the  number  or  the  direction,  or 
both,  of  the  lines  of  force  cut  by  it  are  varied,  a  current  will  be  pro- 
duced. This  happens  if  the  ring  be  turned  round  an  axis  at  right 
angles  to  the  direction  of  the  lines  of  force,  as  shown  in  Fig.  25. 

achieved  by  man,  with  the  possible  exception  of  the  discovery  of  the  expansive  power 
of  steam— is  given  in  his  Experimental  Researches,  i.  7.    See  N.  Y.  Elect.  Eng. ,  xiii.  27. 
•  SILVANUS  P.  THOMPSON  :   Dynamo-Electric  Machinery  (2nd  edition;,  12. 


FIG.  24.    Movement  of  Ring  in  Field  of  Varying 
Intensit}*. 


Transformation  of  Mechanical  Power.         3  r 

This  last  described  organization  is  very  common  in  machines  for 
producing  electricity  from  magnetism.7 

75.  Transformation 
of  Mechanical  Power 
into    Electricity    and 
Heat. — In   thus  moving 
a  closed  circuit  or  loop  of 
wire   through  a  magnetic 
field  so  as  to  cut  across 
the  lines  of  force,  a  cer- 
tain  physical  resistance  is 
encountered,  and  a  corre-      ^ — 
spending  mechanical  force 
must  be  applied  to  over- 
come   it    and    effect    the       FlG'  25'   Circular  Mov^ednt  °f  Ring  in  Uni£orm 
motion.      The    equivalent 

of  mechanical  energy  thus  consumed  reappears  as  electricity  in  the 
closed  ring,  except  that  a  certain  portion,  which  is  transformed  into 
heat,  as  will  be  hereafter  more  fully  explained  (87). 

76.  Direction  of  the  Induced  Current. — It  has  been  stated 
(31),  that  what  we  call   the  direction  of  a  voltaic  current  is   con- 
ventionally assumed  to  be  from  the  positive  pole  of  the  cell  through 
the  conducting  wire  to  the  negative  pole ;  and  it  will  be  obvious  that 
if  the  respective  poles  were  interchanged,  the  current  would  traverse 
the  wire  in  the  opposite  direction.     The  direction  of  the  current  pro- 
duced in  a  conductor  by  moving  it  with  reference  to  the  lines  in  a 
field  of  force,  called  the  magneto-electric  current,  depends  upon  the 
direction  in  which  the  relative  motion  takes  place.     The  law  may  be 
stated  as  follows : 

A  decrease  in  the  number  of  lines  of  force  which  pass  through  or 
are  cut  by  a  closed  circuit,  produces  a  current  round  that  circuit  in 
the  positive  direction  ;  while  an  increase  in  the  number  of  lines  of 
force  which  pass  through  or  are  cut  by  such  circuit,  produces  a  cur- 
rent around  such  circuit  in  the  negative  direction.8 

The  positive  direction  of  the  lines  of  magnetic  force  which  pass 
through  the  loop  of  the  circuit,  is  invariably  associated  with  a  posi- 
tive direction  of  the  current  flowing  round  the  conducting  circuit, 

7  This  and  the  four  following  paragraphs  explanatory  of  the  mutual  reactions  of 
the  magnet,  the  magnetic  field  and  the  conductor,  are  abridged  from  a  portion  of 
chapters  ii.  and  iii.  of  SILVANUS  P.  THOMPSON'S  admirable  work  on  Dynamo- Electric 
Machinery. 

*  SILVANUS  P.  THOMPSON  :  Elementary  Lessons  in  Electricity  aud  Magnetism, 
360- 


32  Sources  of  Electricity. 

just  as  the  forward  thrust  is  with  the  right-handed  rotation  in  the 
operation  of  driving  an  ordinary  right-handed  screw.  This  will  ap- 
pear from  an  examination  of  the  direction  of  the  current  in  the  'ring 
as  shown  by  the  arrows  in  Fig.  25. 

77.  Mutual  Reactions  of  a  Current  and  a  Magnet.— 
The  phenomena  which  have  been  described,  like  most  physical  phe- 
nomena, are  reversible;  that  is  to  say,  a  magnetic  field  may  also  be 
created  by  the  passage  of  an  electric  current  through  a  wire  con- 
ductor, and,  moreover,  a  mass  of  iron  or  steel  situated  in  such  a  field 
will  become  magnetic.     This  effect,  which  is  called  electro-magnetism 
(86,  </),  lies  at  the  foundation  of  electric  telegraphy. 

78.  Summary  of  Magneto-Electric  Phenomena.— It  ap- 
pears, therefore,  from  the  facts  which  have  thus  far  been  stated, 
that: 

(i.)  An  electric  current  is  set  up  in  a  conductor,  either  by  moving 
a  magnet  near  such  a  conductor,  or  by  moving  the  conductor  near  a 
magnet. 

(ii.)  The  establishment  and  maintenance  of  a  continuous  electric 
current  in  a  conductor  requires  a  continuous  expenditure  of  energy, 
or,  in  other  words,  consumption  of  power,  in  order  to  produce  the 
necessary  motion. 

(iii.)  To  induce  currents  in  a  conductor,  there  must  be  relative 
motion  between  conductor  and  magnet,  of  such  kind  as  to  alter  in 
some  manner  the  number  of  lines  of  force  cut  transversely  by  the 
conductor. 

(iv.)  Other  things  being  equal,  the  more  powerful  the  magnetic 
pole  or  magnetic  field,  the  more  powerful  will  be  the  electric  current 
generated. 

(v.)  The  more  rapid  the  relative  motion  of  the  two  elements  the 
more  powerful  will  be  the  current. 

(vi.)  The  direction  of  the  induced  current  depends  upon  the 
direction  of  the  motion  of  the  wire  with  reference  to  the  direction 
of  the  lines  of  force  in  the  field. 

79.  The    Dynamo-Electric    Machine. — A  dynamo-electric 
machine,  briefly  termed  a  dynamo,  in  the  general  and  most  proper 
sense  of  the  term,  embraces  every  machine  capable  of  converting 
the  energy  of  mechanical  motion  into  the  energy  of  an  electric  cur- 
rent, and  it  is  in  this  sense  that  the  term  dynamo  will  hereafter  be 
used  in  this  treatise. 

80.  The   Theoretical    Dynamo. — The   simplest  conceivable 
dynamo  is  illustrated  in  Fig.  26.     It  consists  of  a  single  rectangular 
loop  of  wire,  rotating  in  a  uniform  magnetic  field  maintained  between 


Frictiona I  Electricity. 


33 


the  north  and  south  poles  of  a  large  horseshoe  magnet.  If  the  loop 
be  first  placed  in*  a  vertical  plane,  as  in  the  figure,  the  number  of 
lines  of  force  passing  through  it  will  be  a  maximum,  but  as  it  is 
turned  by  the  crank  into  a  horizontal  position,  the  number  of  inter- 
secting lines  will  obviously  diminish  to  zero.  On  continuing  the 
rotation  beyond  this  point,  the  lines  begin  again  to  thread  through 
the  loop  from  the  opposite  side,  so  that  there  will  be  a  negative  or 
reverse  maximum  when  the  loop  has  been  turned  through  an  angle 
of  180",  or  half-way  round.  During  the  first  half  of  the  revolution, 
therefore,  a  current  will  be  induced  in  the  loop  in  one  direction,  the 
strength  of  which  will  increase  gradually  from  zero  to  maximum  and 
then  diminish  again  to  zero.  Upon  passing  the  180°  position,,  there 
will  begin  an  induction  in  the  reverse  sense,  and  a  similar  effect  will 


FIG  26.     Theoretical  Dynamo-Electric  Machine. 

again  take  place,  resulting  in  the  induction  of  a  current  in  the  loop 
in  the  opposite  direction,  the  operation  being  completed  when  the 
loop  has  been  carried  through  one  complete  revolution. 

81.  Further  considerations,  having  reference  to  the  construction 
and  mode  of  operation  of  the  actual  dynamo,  may  profitably  be  post- 
poned  until  the  student  has  become  familiar  with  the  fundamental 
laws  which  govern   the  flow  and  distribution  of  electric  currents,  as 
the  reaction   of  these  currents   upon   the    machine  which  produces 
them,  though  important,  are  somewhat  complex,  and  in  the  absence 
of  such  knowledge  will  be  found  difficult  of  comprehension  (299). 

82.  Frictional    Electricity.— Frictional    electricity,    which    is 
one  form  of  what  is  termed  static  electricity,  finds  no  practical  applica- 
tion in  telegraphy.     Nevertheless,  the  phenomena  of  static  electricity, 
under  certain  conditions,  manifest  themselves  in  such  a  way  as  to 


34  Sources  of  Electricity. 

interfere  with  the  transmission  and  reception  of  telegraphic  signals, 
and  hence  it  will  become  necessary,  in  connection  with  that  subject, 
to  give  the  matter  further  consideration.  (See  Chapter  VIII.,  §  314.) 
83.  Thermo-Electricity.— This  name  has  been  given  to 
electricity  derived  from  the  direct  conversion  of  heat-energy.  Its 
application  to  telegraphy  has  thus  far  been  purely  tentative,  and 
does  not  require  consideration  here.9 

9  For  an  account  of  thermo-electric  apparatus,  and  its  experimental  application  to 
telegraphy,  consult  LoCKWOOD :  Electricity,  Magnetism,  and  Electric  Telegraphy, 
chap.  iii.  p.  36. 


CHAPTER   IV. 


THEORY    OF    QUANTITATIVE     ELECTRICAL 
MEASUREMENT. 

85.  The  Electric  Current. — It  has  been  stated  (28)  that  a 
conducting  wire  uniting  opposite  poles  of  what,  for  convenience,  we 
call  a  generator  of  electricity,  whether  this  be  a  voltaic  cell  (30)  or  a 
magneto-electric  apparatus  (80),  is  endowed  with  certain  peculiar  prop- 
erties, by  reason  of  which  we  conventionally  assume  an  electric  cur- 
rent to  flow  from  the  positive  to  the  negative  pole  of  such  generator. 

86.  Manifestations  of  the  Current. — The  existence  of  this 
so-called  electric  current  in  the  conjunctive  wire  is  manifested  in 
several  different  ways,  the  most  important  of  which  are  as  follows: 

(a)  If  the  wire  be  dipped  in  iron 
tilings,  a  mass  of  these  will  cluster 
around  it  and  apparently  adhere  to 
it,  appearing  as  in  Fig.  27. 

(fi)  If  the  wire  be  placed  in  the 
immediate  vicinity  of  a  freely  suspended  magnetic  needle  (64),  the  latter 
will  immediately  tend  to  set  itself 
at  right-angles  thereto,  as  indicated 
in  Fig.  28.  Moreover,  the  direction 
in  which  the  needle  moves  will  indi- 
cate the  direction  of  the  current  (31). 
(r)  If  the  wire  be  placed  parallel 
to  another  wire,  or  to  another  por- 
tion of  the  same  wire  which  is  also 
conveying  an  electric  current,  repul- 
sion or  attraction  will  be  manifested 
between  the  two  wires  according  as 
the  two  currents  flow  in  the  same  or 
in  opposite  directions. 


FIG.  27.     Iron  Filings  held  to  Wire  by 
Magnetism. 


FIG.  28.    Deflection  of  Needle  by  Current. 


(d)  If  the  wire  be  wound  spirally  around  a  rod  of  soft  iron,  as  in  Fig.  29, 

the  iron  will  become  a 
magnet,  and  will  con- 
tinue to  be  magnetic  so 
long  as  it  remains  under 
the  influence  of  the  cur- 
rent, but  upon  the  re- 
moval of  the  wire  or  the  cessation  of  the  current,  nearly  every  trace  of 
magnetism  will  disappear  from  the  iron. 

35 


FIG.  29.    Magnetization  of  Soft  Iron  by  Current. 


Quantitative  Electrical  Measurement. 


(e)  If  the  wire  be  severed  and  its  ends  immersed  in  water,  the  water  will  be 
decomposed,  the  oxygen  appearing  at  one  terminal  and  the  hydrogen  at  the 
other,  as  shown  in  Fig.  30.  This  action  is  termed  electrolysis. 

(/)  If  the  severed  ends  of  the  wire  be  united  by  a  very 
thin  wire  of  platinum,  3  in.  or  4  in.  long,  and  this  be 
placed  in  a  vessel  of  alcohol,  a  thermometer  will  show  the 
liquid  to  become  heated  by  the  action  of  the  current  upon 
the  wire  (see  Fig.  31). 

(g)  If  the  ends  of  the  severed  wire  be  placed  side  by 
side  upon  the  tongue,  a  peculiar  taste  will  be  experienced; 
and  if  the  current  be  strong  enough,  it  may  be  felt  by  the 
fingers.  This  sensation  is  termed  an  electric  shock. 

87.  Importance  of  Quantita- 
tive Measurement. — An  accurate 
knowledge  of  the  phenomena  and 

FIG.  30.   Electrolysis  of  Water.         laws  of  electricity,  as  of  everything 

else  in  the  world  around  us,  depends 

primarily  upon  measurement.1     It  is  by  measurement  and  comparison 
alone  that  we  are  able 
to  understand  electrical 
phenomena. 

88.  Fundamental 
Units  of  Mass, 
Space,  and  Time. — 
The  principle  of  the 

1  In  physical  science,  a  first 
essential  step  in  the  direction 
of  learning  any  subject,  is  to 
find  principles  of  numerical 
reckoning,  and  methods  of 
practically  measuring  some 
quality  connected  with  it.  I 
often  say  that  when  you  can 
measure  what  you  are  speak- 
ing about  and  express  it  in 
numbers,  you  know  something 
about  it ;  but  when  you  can- 
not measure  it,  when  you  can- 
not express  it  in  numbers,  your 
knowledge  is  of  a  meagre  and 
unsatisfactory  kind  ;  it  may  be 
the  beginning  of  knowledge, 
but  you  have  scarcely  in  your 
thoughts  advanced  to  the  state 
of  science,  whatever  the  mat- 
ter may  be.— SIR  WILLIAM 
THOMSON  :  Popular  Lectures 
and  Addresses,  p.  73. 


FIG.  31.     Development  of  Heat  by  Electric  Current. 


Absolute  System  of  Measurement.  37 

absolute  measurement  of  electricity  and  magnetism  is,  as  Thomson 
remarks,  "  merely  an  extension  of  the  astronomer's  method  of  reck- 
oning mass  in  terms  of  what  we  may  call  the  universal  gravitation 
unit  of  matter,  and  of  the  reckoning  of  force  adopted  by  astrono- 
mers, in  common  with  all  workers  in  mathematical  dynamics,  accord- 
ing to  which  the  unit  of  force  is  that  force  which,  acting  on  a  unit  of 
mass  for  a  unit  of  time,  generates  a  velocity  equal  to  the  unit  of  velocity* 

89.  Illustration  of  the  Absolute  System  of  Measure- 
ment.— As  a  concrete  example,  suppose  we  take  a  pound  weight 
as  our  unit  of  mass,  and  allow  it  to  drop  through  space  for  a  period 
of  one  second,  our  unit  of  time.     This  mass  will  always  fall  through 
the  same  space  during  the  unit  of  time,  and  at  the  end  of  that  time 
will  be  capable  of  striking  with  a  certain  determinate  force,  which  is 
obviously  measurable  by  an  equivalent  weight,  and  which  therefore 
becomes  our  unit  of  force,  while  the  distance  through  which  the  mass 
falls  in  one  second  becomes  our  unit  of  spaced     Such  a  system  of 
measurement  being  wholly  independent  of  the  physical   properties 
of  any  arbitrary  material,  is  properly  called  an  absolute  system. 

90.  Derivation  of  Electrical  and  Magnetic  Units. — The 
actual  units  used  in  the  measurement  of  electricity  and  magnetism, 
are   founded   upon   the   French    or  metric  system  of  weights    and 
measures,  which  has  been  commercially,  adopted  by  all  the  civilized 
countries  of  the  world  except  Great  Britain  and  the  United  States, 
and  is  in  extensive  use  in  the  last  named  countries  among  scientific 
men.     In  electro-magnetic  measurement,  therefore,  the  centimetre  has 
been  adopted  as  the  unit  of  space,  thegrtm  the  unit  of  mass  or  weight, 
and  the  mean  solar  second  the  unit  of  time.     This   is  briefly  denom- 
inated the  e.g.  s.  (centimetre-gram-second)  system.4 

91.  The  C.  G.  S.  Units  of  Force  and  Work.— The  act  of 
moving  a  weight  of  i  gram  through  a  space  of  i  centimetre,  during 
the  time  of  i  second,  requires  a  perfectly  definite  and  measurable 

*  The  units  of  space,  mass,  and  time,  have  been  selected  by  common  consent  to 
ierve  as  fundamental  units.  Other  units,  for  practical  use,  determined  from  these, 
such  for  example  as  the  unit  of  force,  are  termed  derived  units. 

3  In  making  this  general  statement,  the  effect  of  the  resistance  offered  by  the  air  has 
been  neglected  (this  being,  of  course,  greater  for  a  less  dense  than  for  a  more  dense 
body),  as  has  also  the  fact  that  a  given  mass  which  weighs  a  pound,  for  example  at 
Washington,  D.  C.,  will  weigh  more  than  a  pound  at  the  north  or  south  pole  of  the 
earth,  and  less  than  a  pound  at  Panama,  or  at  the  equator.  This  is  due  to  the  fact 
that  the  earth  is  not  a  perfect  sphere. 

«  The  centimetre  is  somewhat  less  than  half  an  inch  English  measure ;  i  foot  is  very 
nearly  30.5  centimetres  ;  i  cubic  centimetre  of  water  weighs  i  gram  ;  i  oz.  is  very  nearly 
28  grams ;  i  Ib.  is  454  grams ;  the  5-cent  nickel  of  the  1873  U.  S.  coinage  weighs 
exactly  5  grams  and  has  a  diameter  of  2  centimetres ;  the  silver  dime  weighs  2.5  grams. 


38  Quantitative  Electrical  Measurement. 

amount  of  force,  which  is  termed  a  dyne.  The  dyne,  therefore,  is 
the  unit  of  force  in  the  c.  g.  s.  system,  and  is  defined  as  the  force, 
which  acting  upon  a  gram  for  a  second,  generates  a  velocity  of  a  centi- 
metre per  seconds  Any  force  may  be  stated  to  be  equal  to  so  many 
dynes.  A  megadyne  is  equal  to  1,000,000  dynes  (123,  note). 

The  erg  is  the  unit  of  work  in  the  c.  g.  s.  system,  and  is  the  work 
done  by  a  force  of  i  dyne  acting  through  a  distance  of  i  centimetre,  irre- 
spective of  the  time  occupied? 

Now  if  a  force  of  i  dyne  be  applied  to  move  a  closed  conducting 
ring  a  distance  of  i  centimetre  through  a  uniform  magnetic  field  (as, 
for  example,  the  magnetic  field  of  the  earth),  in  the  manner  explained 
in  (73),  work  is  done;  an  electrical  force  is  set  up  in  that  conductor 
which  would  be  the  exact  electrical  equivalent  of  the  mechanical  force 
of  i  dyne,  were  it  not  that  some  part  of  the  original  force  is  unavoid- 
ably transformed  into  heat  during  the  operation.  Neglecting  the 
value  of  the  heat-loss,  this  quantity  of  electricity  is  capable  of  doing 
mechanical  work  equal  to  i  erg,  as,  for  instance,  by  forcibly  deflect- 
ing a  magnetic  needle  (86,  b)  or  by  attracting  the  armature  of  a 
magnet  (86,  d). 

92.  The  Conservation  of  Force. — This  is  one  illustration  of 
the  great  principle  of  the  indestructibility  or,  as  it  is  commonly 
called,  the  conservation  of  force?  which  is  so  important,  that  it  has 
been  justly  remarked  that  the  whole  of  natural  philosophy  is  merely 
a  commentary  upon  it.8 

It  follows  from  this  principle,  that  whenever  a  signal  is  produced 
at  any  point  by  electrical  action,  a  physical  effect  must  be  made  to 
take  place,  and  this  necessarily  involves  the  expenditure  of  some 
form  of  force  at  some  other  point.  It  may  be  the  force  of  chemical 
affinity  in  the  voltaic  cell ;  or  it  may  be  the  force  of  steam  or  of  fall- 
ing water,  or  of  human  muscles  exerted  upon  a  dynamo-electric 

5  EVERETT  :   Units  and  Physical  Constants,  pp.  22,  167. 

6  EVERETT  :   Units  and  Physical  Constants,  p.  167. 

7  DANIELL  :  Principles  of  Physics,  7. 

8  This  doctrine  teaches  that  the  total  amount  of  force  in  the  universe  is  unalter- 
able, and  that  it  can  neither  be  created  nor  destroyed.     Force,  however,  may  appear 
in  a  variety  of  different  forms,  and  is  capable  of  being  readily  changed  from  one  form 
to  another,  but  every  such  mutation  is  nevertheless  rigidly  subject  to  quantitative  laws. 
A  given  amount  of  one  form  of  force  produces  a  definite  quantity  of  one  or  more  other 
forms  of  force  and  no  more.     Hence  this  law  is  sometimes  called  the  equivalence  of 
forces.     This  important  and  interesting  subject  is  well  worthy  of  further  study,  and 
among  special  works  relating  to  its  various  aspects,  the  author  ventures  to  specially 
commend  the  following : — TYNDALL  :   Heat  as  a  Mode  of  Motion  ;   YOUMANS  :  The 
Correlation  and  Conservation  of  Forces ;  a  collection  of  papers  by  Grove,  Helmholtz, 
Mayer,    Faraday,   and  others;    STEWART:    On    the   Conservation  of  Energy ;   and 
SPE AGUE  :  Electricity,  its  Theory,  Sources,  and  Applications. 


Electric  Field  of  Force. 


39 


machine,  but  in  every  case,  the  force  expended  must  be  equal  to 
that  which  is  utilized,  plus  that  which  is  transformed  into  heat  in  the 
course  of  the  operation.  Telegraphic  signals  are  usually  produced 
by  means  of  the  attraction  of  an  armature  by  an  electro-magnet. 
The  initiation  and  maintenance  of  this  attraction  involves  the  consump- 
tion in  the  battery  of  a  perfectly  definite  and  well  ascertained  quantity 
of  material,  which  can  never  be  less  than  the  full  equivalent  of  the 
mechanical  work  done,  but  must  be  somewhat  more,  and  may  pos- 
sibly be  very  much  more,  for  by  unskillful  arrangements  an  undue 
proportion  of  the  original  force  may  be  turned  into  heat  and  ren- 
dered unavailable  for  the  purpose  in  hand  (154). 

93.  Electric  Field  of  Force.— If  we  take  a  magnetic  needle, 
which,  as  we  have  seen,  tends  to  remain  in  the  magnetic  meridian, 
and  place  parallel  to  it  a  wire,  traversed,  as  shown  in  Fig.  28,  by  a 
current  in  the  direction  of  the  arrows,  the  needle  will  seek  to  place 
itself  at  right-angles  to  the  wire  (86,  b\  but  being  under  the  influence 
of  two  antagonistic  forces,  it  will  come  finally  to  rest  in  an  interme- 
diate position.  This  experiment  shows  that  a  conductor,  when  con- 


FIG.  32.     Spectrum  of  Field  Surrounding  Conductor. 

veying  a  current,  is  surrounded  by  a  field-of-force  of  the  same  char- 
acter as  that  which  we  have  found  to  surround  the  magnet  (69).  To 
determine  the  position  and  direction  of  the  lines  of  force  in  this 
field,  we  may  adopt  the  same  expedient  as  in  the  case  of  the  magnet. 


40  Quantitative  Electrical  Measurement, 

Pass  the  conducting  wire  at  right-angles  through  a  piece  of  glass  or 
card-board.  If  iron-filings  be  dusted  into  the  field,  they  will 
arrange  themselves  in  concentric  circles  (Fig.  32),  showing  that  the 
.lines  of  force  encircle  the  wire,  instead  of  radiating  outwardly  from  it  as 
they  did  in  the  case  of  the  magnet.  It  is  these  lines  of  force  which 
act  upon  the  needle  and  tend  to  set  it  at  right-angles  to  the  wire,  for 
when  any  concentric  line  passes  through  both  poles  of  the  needle,  the 
latter  must  set  itself  at  right-angles  to  the  radii  of  the  circle  (71). 

94.  Relation  of  Current  Force  to  Mechanical  Force. — 
The  particular  angular  position  of  a  needle  under  the  influence  of 
a  current  must  necessarily  depend  upon  the  ratio  between  the 
strength  of  the  magnetic  field-of- force  due  to  the  current,  and  that  of 
the  field-of-force  due  to  the  magnetism  of  the  earth,  which  may  be 
regarded  as  sensibly  constant  in  any  particular  locality. 

That  portion  of  the  force  of  the  earth's  magnetism  which  acts  to  hold  a 
horizontal  needle  in  the  meridian  is  called  its  horizontal  component  (H).  Its 
value  varies  from  a  maximum  at  the  magnetic  equator  to  nothing  at  the 
magnetic  poles.  Its  locality  of  greatest  intensity  is  in  lat.  o°  and  long.  101° 
W.,  where  it  is  equal  to  0.3733  dynes.  Following  are  some  determinations 
of  its  value  by  observers  of  the  U.  S.  Coast  and  Geodetic  Survey: 

Washington,   D.  C /. 0.2026  dynes. 

New  York 0.1872 

Eastport,  Me 0.1573  " 

Key  West,  Fla 0.3055  " 

Cincinnati,  0 0.2111  " 

San  Francisco,  Cal 0.2533  " 

St.  Paul  Island,  Alaska 0.2008 

Toronto,  Ont o.  1654  ' ' 

City  of  Mexico o.  3429  ' ' 

(Rep't  U.  S.  C.  &  G.  S.,  1885  ;  App.  No.  6.)  This  report  gives  the  value 
of  the  horizontal  intensity  found  in  over  1,500  observations  in  various  parts 
of  North  America,  reduced  to  the  epoch  of  1885. 

The  value  of  the  horizontal  intensity  is  subject  in  most  places  to  a  slow 
annual  variation.  Along  a  line  drawn  from  British  Columbia  to  Florida, 
the  intensity  is  constant  ;  east  of  this  line  it  shows  an  annual  increase,  and 
west  of  the  line  an  annual  decrease.  {Rep.  U.  S.  C.  &*  G.  S.,  1885,  p.  271, 
and  charts.]  9 

As  the  strength  of  the  field,  due  to  the  current,  is  always  strictly 
proportionate  to  the  capacity  of  the  current  to  produce  other  physical 
effects,  we  have  a  means,  not  only  of  comparing  the  forces  of  diflfer- 

9  The  refined  methods  of  determination  used  are  fully  described  by  C.  A.  SCHOTT 
in  App.  8  of  the  same  for  1881.  For  an  elementary  explanation  of  these  methods  see 
TROWBRIDGE  :  New  Physics,  p.  142.  See  also  A.  GRAY  :  Absolute  Measurements  in 
Electricity  and  Magnetism,  p.  5  ;  F.  E.  NIPHER  :  Theory  of  Magnetic  Measurements, 
P-  46. 


Tkc  Galvanoscope  and  the  Galvanometer.      41 

ent  currents,  but,  by  comparison  with  the  earth's  magnetism,  of 
determining  the  actual  dynamic  value  of  any  current,  in  terms  of  the 
fundamental  units  of  space,  mass,  and  time  (91). 

A  unit  magnetic  pole  weighing  i  gram,  and  free  to  move  in  a 
horizontal  plane,  under  the  action  of  the  earth's  horizontal  force, 
would  require,  at  the  end  of  i  second,  a  velocity  equal  to  202.6 
centimetres  per  second,  if  the  experiment  were  made  in  Washington, 
D.  C.  (See  p.  40.) 

95.  The  Galvanoscope  and  the  Galvanometer. — A  mag- 
netic needle  provided  with  a  conductor  through  which  a  current  may 
be  passed  in  order  to  deflect  it  from  the  meridian  (86,  /;),  is  called  a 
galvanoscope  or  detector.     When  to  these  is  added  a  graduated  scale 
or  dial,  the  instrument  becomes  a  galvanometer.     In  order  that  the 
angle  of  deflection  of  a  needle  under  the  influence  of  any  current 
shall  bear  a  definite  ratio  to  the  value  of  such  current,  certain  pre- 
cautions in  its  mechanical  construction  are  necessary  to  be  observed. 
It  is  essential  that  the  field  produced  by  the  current  should,  like  that 
of  the  earth,  be  so   large  in  comparison  with  the  needle,  that  the 
motion  of  the  latter  within  it,  when  deflected,  shall  not  appreciably 
change  its  relation  to  the  entire  field. 

96.  Tangent  Galvanometer. — In  this  instrument  the  forego- 
ing  condition   is  fulfilled.     In    its   most  simple    form,  the   tangent 


FIG.  33.     Needle  in  Circular  Loop. 

galvanometer  consists  of  a  single  circular  turn  or  loop  formed  in  the 
conducting  wire  ;  in  the  center  of  the  loop  is  suspended  the  needle, 
which  in  length  should  not  exceed  -^  the  diameter  of  the  loop. 
Such  an  organization  is  shown  in  Fig.  33,  in  which  n  s  is  the  sus- 
pended needle,  and  P  N  the  looped  conductor  which  surrounds  it. 


42  Quantitative  Electrical  Measurement. 


The 


principle  of  action  may  be  understood  by  reference  to  Fig.  34. 

Let  the  magnetic  needle  n  s  be  sus- 
pended    in    the    earth's    magnetic 
meridian    N  S.     If  now    the    con- 
ducting wire  or  loop  be  placed  in 
the  plane  of  N  S,  and  we  suppose 
this  wire  to  be  traversed  by  a  cur- 
rent capable  of  producing  a  mag- 
netic field  precisely  equal  in  strength 
to  that  of  the  earth,  the  needle  will 
swing  toward  a  position  represented 
by  the  line  A  B,  at  right  angles  (or 
90°)  to  the  one  originally  occupied. 
But  the  two  antagonistic  forces  being 
equal,  the  needle  will  come  to  rest 
in  a  position    half-way  between    N 
and  B,   called   the    resultant.     This 
coincides  with  the    line  Ai,  which 
forms  an  angle  of  45°  with  the  zero 
or  o°  line  N  S.     Now  if  we  double 
the  strength  of  the  current,  and  con- 
sequently that  of  the  field  produced 
by  it,  it  will  partially  overpower  the 
earth's  field,  and  the  needle  will  as- 
sume the  position  corresponding  to 
the  line  A2,  which  is  an   angle   of 
63^°  nearly.     If  we    again    double 
the  strength  of  the  current,  we  shall 
increase  the  deflection  to  76°,  repre- 
sented by  the  line  A4-      In  geomet- 
rical language,  the  line  N4  is  termed 
tangent   to    the   arc  or 
quadrant  N  B  of  the 
circle.     The  circle 
being  divided  in- 
to    360°,     the 
tangent,    as 
found    in    a 
computed 
'.     table     of 
S  natural  tan- 

FIG.  34.    Principle  of  Tangent  Galvanometer.  gents     (see 


Character  of  Electrical  Measurements.         43 

page  55),  will  always  be  proportionate  to  the  strength  of  the  current 
by  which  the  corresponding  deflection  was  caused.  The  actual  con- 
struction of  this  useful  instrument  will  be  described  in  detail  else- 
where (102). 

97.  Character  of  Electrical  Measurements.— The  qualities 
of  an  electric  current  by  virtue  of  which,  as  we   have  seen,  it  is 
enabled  to  exert  force,  to  produce  physical  effects,  or,  in  technical 
language,  to  do  work,  are  three  in  number,  viz:   (i)  quantity,  vari- 
ously called  volume,  or  strength  of  current;   (2)  potential,  variously 
called  pressure,   tension,  and  intensity,10  and   (3)  duration,  or  time 
occupied  in   doing  the   work.     The  value  of  the  first  two  of  these 
properties,  in  the  case  of  any  particular  current,  is  dependent  not  only 
upon  the  circumstances  of  its  origin,  but  upon  the  special  character- 
istics of  the  conductors  which  the  current  is  compelled  to  traverse. 
Hence  there  are  two  distinct   classes  of  electrical   measurements: 

(1)  those  which  are  applied  directly  to  electricity  itself,  either  in  a 
static  or  in  a  dynamic  condition,  that  is  to  say,  as  a  stationary  charge 
or  as  a  flowing  current,  and  (2)  those  which  are  applied  to  the  con- 
ductor which  a  current  is  or  may  be  compelled  to  traverse. 

98.  Characteristics  Capable  of  Measurement.— Electricity 
itself,  whether   in  a  static  or  a  dynamic  condition,  has  but  three 
properties  susceptible  of  quantitative  measurement,  viz  :   (i)  quantity, 

(2)  potential,  and  (3)  duration.     Electric  conductors  have  four  quali- 
ties which  may  affect  the  value  of  the  currents  which  traverse  them, 
and  which,  in  like   manner,  are   susceptible   of  measurement,   viz : 
(4)  magnitude  (length,  breadth,  and  thickness),  (5)  weight,  or  mass, 
(6)  temperature,  and  (7)  conductivity,  or  the  reciprocal  of  this,  called 
resistance.     All  these  considerations  must  be  taken  into  account  in 
performing  any  electrical  measurement. 

99.  Apparatus  for  Measurement.— A  complete  apparatus  for 
executing  electrical  measurements  must  therefore  comprise : 

(a)  A  meter  for  quantity  of  current. 

(b)  A  meter  ior  potential  of  current. 

(c)  A  chronometer  for  time. 

(d)  A  scale  for  linear  measure. 

(e)  A  scale  or  balance  for  weight. 

(f)  A  thermometer  for  temperature. 

(g)  A  standard  of  electrical  conductivity  or  resistance. 

10  The  French  scientific  writers  have  always  been  accustomed  to  use  the  term  *'»- 
tensite  in  the  sense  in  which  we  use  the  term  quantity  or  volume.  The  frequent  trans- 
lation of  this  word  by  the  English  term  "  intensity,"  which  has  in  fact  a  wholly  differ- 
ent signification,  has  been  the  cause  of  no  little  confusion  in  electrical  literature. 


44  Quantitative  Electrical  Measurement. 

Not  all  these  instruments  are  required  in  making  every  measure- 
ment, for  one  or  more  of  the  unknown  conditions  may  be  arbitrarily 
assumed,  or  they  may  be  determined  from  others  which  are  known, 
as  we  shall  hereafter  frequently  have  occasion  to  note. 

100.  The  Ammeter,  Voltameter,  and  Calorimeter. — The 
instrument  for  measuring  quantity  of  current  need  not  necessarily  be 
a  galvanometer,  although  in  telegraphic  work  this  is  used  practically 
to  the  exclusion  of  everything  else.  Currents  may  also  be  measured 
by  the  attractive  force  of  an  electro-magnet  (83,^),  as  in  the  instru- 
ment called  the  ammeter,  or  by  ascertaining  the  volume  of  gas 
evolved  in  a  unit  of  time  (83,*?),  in  which  case  the  instrument  is  called 
a  voltameter,  or  by  measuring  the  heat  developed  in  a  unit  of  time 
(83,/),  in  which  case  it  is  called  a  calorimeter.  All  these  instruments 
find  frequent  use  in  general  electrical  investigations,  but  are  less 
convenient  than  the  galvanometer  for  measurements  in  connection 
with  telegraphy. 


CHAPTER   V. 

THE   LAWS   AND   CONDITIONS  OF   ELECTRICAL  ACTION. 

101.  Apparatus  Required  by  the  Student.— The  student 
who  desires  to  obtain  a  thorough  knowledge,  not  only  of  the  art  of 
telegraphy,  but  of  the  principles  of  physics  and  chemistry  upon  which 
that  art  is  based,  is  earnestly  advised  to  supply  himself,  in  the  first 
instance,  with  his  own  apparatus.  The  comparatively  small  cost  of 
the  necessary  outfit  will  be  many  times  repaid  in  the  value  of  the 
clear  and  definite  experimental  knowledge  which  this  means  alone 
will  enable  him  to  acquire.  It  is  for  many  reasons  advisable  that 
two  students  should  work  together,  as  experience  has  shown  that  the 
study  is  rendered  far  more  interesting,  and  that  much  more  rapid 
and  intelligent  progress  may  be  made  in  this  way.  The  following 
list  of  apparatus  and  supplies  will  serve  the  requirements  of  two 
students,  the  approximate  cost  of  each  item  being  given  : 

4  cells  "crowfoot"  battery  complete,  with  4  copper  connect- 

ors (9) $0.75  $3.00 

2  keys  (258) 1.75  3.50 

2  5-ohm  sounders  (261) 2.25  4. 50 

2  Ibs.  No.  18  "  burglar  alarm  "  insulated  copper  wire 35  .70 

2  feet  f-in.  rubber  tubing  for  gravity  cell  (39) .30 

i  2-in.  glass  funnel  for  gravity  cell  (39) .10 

i  hydrometer  (18) .50 

i  battery  brush  (40) .25 

i  6-in.  permanent  magnet  (67) .60 

5  Ibs.  sulphate  copper 10  .50 

i  box  No.  2  office-wire  staples .10 


Total  for  two  students $14.05 

102.  Construction  of  the  Tangent    Galvanometer. — A 

tangent  galvanometer  and  rheostat  are  almost  absolutely  necessary 
in  the  experimental  investigation  of  electrical  action,  and  hence  it  is 
to  be  regretted  that  a  sufficiently  cheap  but  good  apparatus  of  this 
kind  has  never  been  made  available  for  the  use  of  students  and  ama- 
teur electricians.  It  is  nevertheless  quite  possible  for  an  ingenious 
person,  somewhat  accustomed  to  mechanical  tools  and  processes,  to 


46     Laws  and  Conditions  of  Electrical  Action. 

construct,  at  a  trifling  cost,  apparatus  sufficiently  accurate  for  all 
practical  purposes. 

The  following  directions  for  making  a  tangent  galvanometer  are 
taken  in  part  from  S.  R.  BOTTONE'S  Electrical  Instrument  Making  for 
Amateurs. 

103.  First  a  ring  of  hard  wood  C  is  accurately  turned  in  a  lathe, 
of  the  form  and  dimensions  shown  in  Figs.  35  and  36.  The  channel 


FIG.  35.    Elevation  of  Tangent  Galvanometer. 

in  the  edge  of  the  ring  must  be  of  such  depth  that  the  bottom  of  it 
will  be  exactly  6  in.  in  diameter  and  \  in.  in  breadth.  Such  a 
channel  will  hold  38  turns  (in  2  layers)  of  No.  22  "American 
gauge "  double  cotton-covered  copper  wire.  The  coil  will  require 
62  feet  of  wire,  weighing  about  2  oz.,  and  costing  about  25  cents. 
The  wire  must  be  wound  carefully  and  accurately  in  the  groove  or 
channel  (this  may  be  best  done  in  a  lathe),  and  the  ends  brought 


Construction  of  the  Tangent  Galvanometer.     47 


out  through  small  holes  in  opposite  sides  of  the  ring  and  through  the 
base,  as  shown  in  Fig.  36.  The  ring  and  the  wire,  being  first  well 
dried,  should  be  thoroughly  coated  with  shellac  varnish. 


Scale  M  actual  size. 
FK;.  36.    Cross-section  of  Tangent  Galvanometer. 

The  base  B  may  be  of  hard  wood,  preferably  turned,  7  in.  in 
diameter  and  i  in.  thick.  It  is  supported  upon  3  equidistant  level- 
ing screws  /  /,  which  may  be  common  screw-eyes  (preferably  of  brass, 
though  iron  will  answer),  with  the  sharp  tips  filed  off. 

The  ring  C  is  fixed  firmly  in  a  vertical  position  upon  the  base  B, 
taking  care  that  it  is  placed  accurately  at  right  angles  therewith.  A 
recess  may  be  cut  in  the  base,  the  ring  being  let  into  it,  and  secured 
by  a  clamping  piece  b  of  wood,  made  fast  to  the  base  B  by  two  brass 
screws  s. 

The  magnetic  needle,  N  S,  Fig.  37,  may  be  of  a  piece  of  watch- 
spring  i  in.  long  and  \  in.  wide.  Soften  this  by  holding  it  in  the 
flame  of  a  spirit-lamp  until  of  a  dull  red  color,  and  then  allow  it  to 


48     Laws  and  Conditions  of  Electrical  Action. 


FGk?vknometlr  (Fuiisie. 


cool  slowly.  Drill  a  hole  exactly  in  the  cen- 
ter about  fa  in.  in  diameter,  and  file  the  ends 
into  the  tapering  form  shown.  Straighten 
the  needle  with  a  hammer,  and  unless  its 
center  of  gravity  corresponds  with  the  center 
of  the  hole,  correct  the  error  by  filing  the 
heavy  part  away.  Next  harden  the  needle 
by  reheating  it  in  the  lamp-flame  until  nearly 
red-hot,  and  dropping  it  into  cold  water.  It 
must  then  be  magnetized,  by  rubbing  each 
half  separately  from  the  center  to  the  end, 
with  a  permanent  magnet  (67),  being  very  care- 
ful to  rub  one  end  with  one  pole  of  the  mag- 
net, and  the  other  end  with  the  opposite  pole. 
A  jeweled  center  is  then  fitted  to  the  hole 
in  the  needle,1  and  secured  with  glue,  or 
better,  with  white  or  red  lead  used  as  a  ce- 
ment. It  is  not  difficult  for  the  amateur  to 
make  a  center  out  of  glass,  in  case  a  jeweled 
one  cannot  be  procured,  by  holding  a  piece 
of  |  in.  glass  tube  in  the  spirit-lamp  flame, 
and  pulling  it  apart  lengthwise  as  soon  as  it 
softens.  In  Fig.  38  this  operation  is  illus- 
trated at  C.  E  is  one  of  the  two  pieces, 
which  will  be  drawn  out  as  shown,  into  a 
thread-like  extremity.  Fuse  this  thin  end  in 
the  flame  and  a  little  globule  will  be  formed, 
the 


closing  the  bore  of 
tube  as  at  F.  When  cold 
the  tube  can  be  broken 
off  by  cutting  a  scratch  at 
the  desired  point  with  a 
triangular  file.  This  leaves 
a  center,  G,  adapted  to 
support  the  needle  freely 
upon  a  pivot  as  shown  in 
Fig.  13,  page  25. 

Having  fixed  the  cen- 
ter in  the  hole  in  the  nee- 
dle as  directed,  poise  the 

whole   Upon   the   point  Of  FIG.  38.    Method  of  making  Glass  Center. 

i  Needles  fitted  with  jeweled  centers  are  sold  by  E.  Goldbacher,  98  Fulton  St.,  N.Y. 


Construction  of  the    Tangent  Galvanometer.     49 

a  common  sewing  needle  as  a  pivot,  and  if  the  magnetic  needle  is 
found  not  to  balance  so  as  to  lie  in  a  laterally  horizontal  position, 
adjust  the  center  before  the  cement  has  firmly  set.  If  one  end 
of  the  needle  appears  heavier  than  the  other,  load  the  light  end 
with  a  touch  of  melted  sealing-wax,  applied  to  the  under 
side. 

Procure  a  fine  straight  straw,  3^  in.  long,  and  make  a  transverse 
hole  through  the  middle  of  it  with  a  large  pin  ;  thrust  the  top  of  the 
glass  center  carefully  through  this  hole,  so  that  the  straw,  which  is 
to  serve  as  an  index  or  pointer,  will  lie  exactly  at  right-angles  with 
the  magnetic  needle  (Fig.  37).  Secure  the  straw  to  the  glass  center 
with  a  mere  trace  of  glue,  and  set  it  away  to  dry. 

Make  a  dial  of  card-board  like  Fig.  39  (which  shows  one  half  of 
it),  one  half  being  graduated  in  degrees  and  the  other  half  divided 


FIG.  39.     Half  of  Card-board  Dial  of  Tangent  Galvanometer. 

in  tangents,  upon  the  principle  explained  in  (96).  The  outer  circle 
should  be  3J-  in.  in  diameter.  Next  cut  out,  in  a  lathe  if  possi- 
ble, a  circular  hole  4  in.  in  diameter  in  a  circular  piece  of  hard 
wood  H,  5  in.  diameter  and  i  in.  thick,  and  then  enlarge  this  hole 
T3g-  in.  all  round  with  a  shoulder  \  in.  deep,  as  shown  in  the  cross- 
section,  Fig.  36. 

Make  a  bridge-piece  D  of  hard  wood,  i  in.  thick,  and  secure  it  to 
the  base  by  brass  screws  as  shown  in  Fig.  35.  This  bridge-piece 
should  be  just  high  enough  so  that  the  center  of  the  magnetic  needle 
N  S  will  come  exactly  in  the  geometrical  center  of  the  vertical  ring 
C  containing  the  wire.  The  circular  board  G  is  secured  to  the 
bridge-piece  D  with  brass  screws,  the  sewing-needle  (point  upward) 
inserted  into  it  for  a  pivot,  and  the  card-board  dial  secured  thereto 


50     Laws  and  Conditions  of  Electrical  Action. 


by  small  brass  or  copper  tacks,  in  such  position  that  when  the 
magnetic  needle  is  in  the  plane  of  the  vertical  ring,  the  straw  will 
point  to  zero  upon  the  scale  at  each  end.  The  horizontal  wooden 
ring  H  is  now  laid  upon  the  dial  and  fastened  in  place  with  brass 
screws.  A  circular  piece  of  glass  g  is  cut  to  the  right 
size  to  lie  upon  the  shoulder  of  the  ring  H,  and  may 
be  secured  in  place  by  an  elastic  ring  r  of  stout  brass 
wire,  cut  to  the  right  length,  so  that  it  may  be  sprung 
into  place  over  the  glass,  and  within 
the  wooden  ring,  after  the  needle  is 
in  place. 

If  pieces  of  mirror  be  let  into  the 
dial,  they  will  materially  aid  in  mak- 
ing accurate  readings  of  the  indica- 
tions, as  the  index  and  its  image 
will  then  appear  coincident  only 
when  the  eye  is  vertically  over  the 
point  observed.  The  error  arising 
from  angular  observations  is  termed 
parallax. 

The  ends  of  the  coil  wire  are  car- 
ried through  holes  into  grooves  cut 
for  the  purpose  on  the  under  side 

of  the  base,  and  thence  to  two  binding-screws,  P  N  (English  pattern), 
Fig.  35,  which  may  be  purchased  for  about  20  cts.  each.  These 
should  be  placed  in  the  plane  of  the  vertical  ring  upon 
opposite  sides  of  the  base,  and  the  ends  of  the  wires 
carefully  soldered  to  them  underneath  the  base. 

Binding-screws   are  brass  clamps  for  conveniently 
attaching  connecting  wires  to  electrical  instruments. 
They  are  made  in  many  patterns,  the  most  common 
types  being  those  shown  in  Figs.  40  and  41.     In  Fig. 
40,  the  wire  is  inserted  into  the  transverse  hole  and 
clamped  by  turning   the   screw.     This  form   is   very 
handy  for  ordinary  purposes,  but  where  a  very  good    FIG.  42. 
contact  is  essential,  as  in  measuring  apparatus,   the 
English  pattern,  Fig.  41,  is  preferable,  the  wire  being 
looped  round  the  stem  and  clamped  by  the  thumb-nut. 
ing  two  or  more  wires,  this  pattern  is  sometimes  made  with  more 
than  one  nut,  as  in  Fig.  42. 

105.     The    accuracy   of  the    above-described    galvanometer    will 


FIG.  40. 

Ordinary 

Binding-Screw 


FIG.  41.  Binding- 
Screw,  English 
Pattern. 


Double 


For  attach- 


Construction of  the  Rheostat. 


depend  largely  upon  the  care  used  in  making  it.  The  most  impor- 
tant point  is  to  make  sure  that  the  centers  of  the  vertical  coil  and 
of  the  magnetic  needle  exactly  coincide,  and  that  the  wire  is  accu- 
rately and  smoothly  wound  upon  the  vertical  ring.  It  is  pos- 
sible for  the  amateur  to  construct  an  instrument  which  will  do  quite 
as  accurate  work  as  those  which  are  sold  for  $50  and  upward  by  pro- 
fessional instrument-makers  (367). 

106.  Construction  of  the  Rheostat. — A  convenient  form 
of  rheostat  for  use  with  the  tangent  galvanometer  is  not  beyond  the 
constructive  skill  of  the  amateur.  Procure  from  a  dealer  a  device 
called  a  "  peg  pole-changer," 


Fig.  43,  with  4  pegs,  which  may 
be  had  for  about  $3.  This  is 
to  be  mounted  upon  the  cover, 


a 


FIG.  43.     Peg  Pole-Changer  and  Peg. 


FIG.  44.    Rheostat  and  Box. 


C,  of  a  wooden  box,  B,  which  is  removably  fastened  by  screws,  as 
shown  in  Fig.  44. 

Procure  also  from  a  dealer  two  lengths  of  double  cotton-covered 
German-silver  resistance  wire,  as  follows : 

13  ft.  of  No.  18  (American  gauge) 0403  in.  diameter. 

40  "    "     "    26  "       0159  in.          " 

Stretch  each  piece  of  wire  out  straight,  double  it  in  the  middle  of  its 
length,  and  wind  smoothly  upon  a  separate  wooden  spool, — a  com- 
mon thread  spool  will  do.  Commence  winding  at  the  bight  or  loop 
c,  and  wind  double  so  that  both  ends  of  the  wire  will  come  on 
the  outside  of  the  coil,  as  at  d  d.  Fasten  the  filled  spools  to  the 
under  side  of  the  box  cover,  C,  with  long  brass  screws,  as  shown  in 
Fig.  44. 

The  ends  of  the  wires  on  the  spools  must  be  uncovered  by 
scraping  off  the  cotton  envelope ;  then  carefully  cleaned  with 
emery  cloth,  and  soldered  with  rosin  to  stout  brass  wires  ww, 


52      Laws  and  Conditions  of  Electrical  Ac  tic 


c 


v 


e) 


which  are  screwed  into  the   brass   plates   supporting  the    binding- 
screws,  precisely  as  indicated  in  Fig.  45.     The  spare  peg-hole  seen 

in  Fig.  43  will  provide  for  a  third 
coil  of  still  higher  resistance  (indi- 
cated in  Fig.  45  in  dotted  lines  at 
the  right),  in  case  one  should  be 
needed.2 

The  thick  wire  coil,  made  as 
above,  will  have  an  approximate 
resistance  of  i  ohm,  and  the  thin- 
ner one  an  approximate  resistance 
of  20  ohms  (125). 

107.  Preparation  for  Ex- 
periments. —  Having  provided 
himself  with  the  necessary  appli- 
ances, the  student  is  now  prepared 
to  undertake  an  experimental  investigation  of  the  laws  of  the  electric 
current.  Four  gravity  cells  should  be  set  up  in  accordance  with 
directions  in  Chapter  II,  using  pure  water  as  directed  in  (21)  and 
not  s.  z.  solution.  Arrange  these  in  some  convenient  place,  as  on  a 


d 


0~ 


FIG.  45.     Connections  of  Rheostat. 


FIG.  46.    Cells  in  Series  with  Tangent  Galvanometer. 

common  kitchen  table,   and  connect  them  with    each    other   as  in 
diagram  Fig.  46,  the  copper  of  one  cell  to  the  zinc  of  the  next,  and 

2  These  resistance-coils,  before  being  mounted,  may  with  advantage  be  dried  for 
several  hours  in  a  hot,  but  not  too  hot,  oven,  and  when  taken  out  should  be  instantly 
immersed  in  a  hot  mixture  in  readiness  for  the  purpose,  composed  of  10  parts  by  weight 
of  rosin  and  i  part  of  white  wax.  Let  the  compound  cool  with  the  coils  in  it,  remov- 
ing the  latter  just  before  it  sets.  Heat  them  again,  if  necessary,  enough  to  remove 
the  surplus  material. 


Effect  of  Varying  Number  of  Cells  in  Series.    53 

the  free  copper  and  zinc  terminals,  by  means  of  pieces  of  copper  wire 
about  3  ft.  long,  to  the  binding  screws  P  N  of  the  galvanometer. 
The  cells  are  now  said  to  be  arranged  in  series,  both  with  each  other 
and  with  the  galvanometer.  At  first,  little  or  no  effect  will  be  ob- 
servable upon  the  needle  of  the  galvanometer ;  but  in  the  course  of  a 
few  hours  a  deflection  may  be  observed,  which  will  slowly  increase. 
Leave  the  apparatus  alone,  except  to  tap  the  galvanometer  occasion- 
ally with  the  finger  to  facilitate  the  movement  of  the  needle,  until  it 
indicates  about  58°,  when  the  cells  may  be  considered  to  be  in  good 
working  condition. 

108.  Effect  of  Varying  Number  of  Cells  in  Series.— Let 
the  student  now  carefully  observe  the  effect  produced  upon  the  needle 
of  the  galvanometer  by  varying  in  the  number  of  cells  in  series  with  the 
coil.  The  results  will  be  found  to  be  something  like  the  following: 


Cells  in  Series. 

Deflection. 

Tangent. 

^8° 

1.  60 

0 

57^° 

i  <;6 

2                                       ... 

e;64-° 

I    ^O 

I       

531° 

I  .  v\ 

As  elsewhere  stated  (96),  the  effective  strength  or  quantity  of  cur- 
rent is  always  in  the  ratio  of  the  tangents  of  the  angles  of  deflection. 
Hence  we  have,  in  the  above  experiment,  the  apparently  paradoxical 
result,  which  is  nevertheless  susceptible  of  rational  explanation 
(132),  that  under  the  conditions  stated,  quadrupling  the  number  of 
the  cells  in  the  circuit  only  increases  the  quantity  of  current  in  the 
ratio  of  135  to  160,  or  about  18  per  cent. 

109.   Cells  in  Parallel  Series.— Next   arrange   the  four  cells 
in  2  series,  with  2  cells  in  each  series,  as  in  diagram,  Fig.  47.     Such 


FIG.  47.    Cells  in  Parallel  Senes. 

an  arrangement  is  termed  parallel  series,  or  sometimes  multiple  series 
This  gives  quite  a  different  result. 

2  series  of  2  cells  each.     Deflection  6gf°  (tangent  2.70). 


UNIVERSITY 


54     Laws  and  Conditions  of  Electrical  Action. 

no.  Cells  in  Parallel. — Finally,  connect  all  the  copper  ter- 
minals to  one  terminal  of  the  galvanometer  and  all  the  zincs  to  the 
other,  as  in  Fig.  48.  This  is  termed  connecting  in  parallel,  or  mul- 
tiple-arc. The  result  will  be  again  different,  as  follows: 

4  cells  in  parallel,  deflection  73^°  (tangent  3.38). 


FIG.  48.    Cells  in  Parallel. 

in.  Increasing  Length  of  Conducting  Circuit.— Leaving 
the  cells  and  the  galvanometer  connected  in  the  manner  last  de- 
scribed, let  the  current  next  be  made  to  pass  also  through  the  length 
of  the  2  Ibs.  of  No.  18  copper  wire,  which  will  be  in  linear  measure 
a  little  over  300  feet.  The  deflection  of  the  needle  will  now  fall 
from  73  J°  to  about  59 J°  (tangent  1.70).  This  experiment  proves 
that  when  the  current  is  made  to  pass  through  the  long  copper  wire, 
under  the  conditions  of  the  experiment,  its  quantity  is  diminished  to 
about  one-half  the  original  amount. 

112.  Next  place  the  galvanometer  in  circuit  with  one  cell,  as  we 
did  once  before,  and  found  the  deflection  to  be  53^°  (tangent   1.35). 
Insert  the  long  copper  wire  in  circuit  with  the  galvanometer  and  cell, 
and  we  get  a  deflection  of  about  44°  (tangent  0.965),  showing  that 
the  quantity  of  current  has  been  diminished  about  one-third. 

113.  Leaving  the  long  copper  wire  still  in  circuit  with  the  galvan- 
ometer, add  another  cell,  making  2  in  series.     The  deflection  now 
becomes  about  51°  (tangent   1.23),  and  by  adding  still  another  cell, 
making    3,    we   get   a   deflection    of  53^°    (tangent    1.35),    exactly 
what  we  had  with  one  cell  when  the  copper  wire  was  not  included 
in  the  circuit. 

114.  Conditions  which  Determine  Quantity  of  Current. 
— From  the  last  experiment  we  arrive  at  two  fundamental  facts  re- 


Table  of  Tangents. 


55 


TABLE     III. 
TANGENTS    FOR  EVERY   HALF   DEGREE. 


Deg. 

o' 

30' 

Deg.     o'       30' 

Deg. 

o' 

30' 

0 

.0000 

.0087 

30     .5774 

.5890 

60 

1.732 

1.767 

i 

•0175 

.0262 

31 

.6009 

.6128 

61 

1.804 

1.842 

2 

•0349 

•0437 

32 

.6249 

.6371 

62 

1.881 

1.921 

3 

.0524 

.0612 

33 

.6494 

.6619 

63 

1.963 

2.0C6 

4 

.0699 

.0787 

34 

•  6745 

.6873 

64 

2.050 

2.096 

5 

.0875 

.0963 

35 

.7002 

.7133 

65 

2.144 

2.194 

6 

.1051 

•1139 

36 

.7265 

.7400 

66 

2.246 

2  3OO 

7 

.1228 

•  1317 

37 

, 
•7536 

.7673 

67 

2.356 

2.414 

8 

.1405 

•1495 

38 

•7813 

•7954 

68 

2.475 

2-539 

9 

.1584 

•1673 

39 

.8098 

.8243 

69 

2.605 

2.675 

10 

.1763 

•1853 

40 

.8391 

.8541 

70 

2.747 

2.824 

ii 

.1944 

•2035 

4i 

.8693 

.8847 

7i 

2.904 

2.989 

12 

.2126 

.2217 

42 

.9004 

.9163 

72 

3.078 

3.172 

13 

.2309 

.2401 

43 

.9325 

.9490 

73 

3.271 

3.376 

14 

•2493 

.2586 

44 

.9657 

.9827 

74 

3.487 

3.606 

15 

.2679 

•2773 

45 

I.OOO 

1.018 

75 

3.732 

3.867 

16 

.2867 

.2962 

46 

1-035 

1.054 

76 

4.011 

4.165 

17 

.3057 

.3153 

47 

1.072 

1.091 

77 

4.331 

4.510 

18 

•3249 

.3346 

48 

I.  Ill 

1.130 

78 

4.705 

4.9J5 

19 

•3443 

•3541 

49 

1.150 

1.171 

79 

5.145 

5-395 

20 

.3640 

•3739 

50 

1.192 

1.213 

80 

5.671 

5.976 

21 

.3339 

•3939 

5i 

1.235 

1-257 

81 

6.314 

6.691 

22 

.4040 

.4142 

52 

1.280 

1.303 

82 

7.115 

7-599 

23 

.4245    .4348 

53 

1.327 

I-35I 

83 

8.144 

8.777 

24 

•4452 

•  4557 

54 

1.376 

1.402 

84 

9.514 

10.39 

25 

.4663 

.4770 

55 

1.428 

L455 

85  •  n-43 

12.71  » 

26 

.4877 

.4986 

56    1.483 

1.511 

86  ;  14.30 

16.35 

27 

•  5095 

.5206 

57 

1.540 

1-570 

87   19.08 

22.90 

28 

•b3i7 

•5430 

58 

1.  600 

1.632 

88   28.64 

38.19 

29 

•  5543 

•  5658 

59    1.664    1.698 

89  j  57-29 

114.6 

56     Laws  and  Conditions  of  Electrical  Action. 

specting  the  electric  current,  which  are  that  its  quantity  may  be 
affected,— -first,  by  varying  the  length  of  the  conductor  which  it 
traverses,  and  second,  by  varying  the  number  of  cells  in  series  in  the 
battery  from  which  the  current  is  derived. 

115.  Resistance. — What  is  true  of  the  copper  wire  is  also  true 
of  all  known  substances, — namely,  that  they  oppose  a  certain  and 
definite  resistance  to  the  passage  through  them  of  an  electric  current, 
and  the  quantity  of  current  which  passes,  other  things  being  equal, 
is  in  every  case  inversely  proportional  to  the  resistance  which  it  en- 
counters in  the  circuit  (127).     In  other  words,,  the  greater  the  resist- 
ance the  less  the  quantity  of  current,  and  vice  versa. 

116.  Conductors    and     Insulators. — Although    all    bodies 
offer  more  or  less  resistance  to  the  passage  of  the  electric  current, 
there  is  an  enormous  difference  in  the  resisting  capacity  of  different 
substances.      Those  which   offer  comparatively  little  resistance  are 
called  in  a  general  sense  conductors   of  electricity,  while  those  that 
offer  great  resistance  are   termed  insulators.      This  distinction,  like 
that,  for  example,  between  heat  and  cold,  is  wholly  relative  and  not 
absolute.      The  most  perfect  known  conductors  offer  some  resistance 
to  the  current,  and  the  most  perfect  insulators  known  permit  some 
current  to  pass.     But  the  actual  difference  in  some  instances  is  al- 
most beyond  the  power  of  the  mind  to  grasp. 

It  is  difficult  to  find  any  comparison  which  will  give  a  tolerably  good  idea 
of  the  extraordinary  difference  between  the  electrical  resistance  of  these  two 
materials  (copper  and  gutta-percha).  It  is  about  as  great  as  the  difference 
between  the  velocity  of  light  and  that  of  a  body  moving  through  one  foot  in 
6700  years  ;  yet  the  measurements  of  the  two  quantities  are  daily  made  with 
the  same  apparatus  and  the  same  standards  of  comparison.  This  fact  is 
well  calculated  to  give  an  idea  of  the  range  of  electrical  measurements,  and 
the  perfection  to  which  the  instruments  employed  have  been  brought. — 
FLEEMING  JENKIN  on  Submarine  Telegraphy,  in  North  British  Review* 
December,  1866. 

117.  The  division  of  bodies  into  the  two  classes  of  conductors 
and  insulators,  though  in  a  certain  sense  arbitrary,  is  very  conven- 
ient in  practice.     In  telegraphy,  the  term  conductor  is  applied  to- 
all  substances  which  are  used  in  any  manner  as  a  portion  of  the 
conducting  circuit,  while    on    the    other   hand,  the    term    insulator 
is  applied  to  all  substances  which  are  employed  to  confine  the  elec- 
trical current  to  such  conductors,  by  preventing  its  escape  in  unde- 
sired  directions.     Following  is  a  list  of  some  of  the  substances  so 
used,  arranged  as  nearly  as  possible  in  the  order  of  their  specific 
conductivity : 


Specific  Resistance  of  Different  Metals.         57 


CONDUCTORS. 


INSULATORS. 


I.  Copper. 

15.   Metallic  oxides. 

2.  Zinc. 

16.  Ice  (dry). 

3.   Platinum. 

17.   Paper  (dry). 

4.  Iron. 

18.  Wood  (dry). 

5.  Nickel. 

19.  Earth  (dry). 

6.  Tin. 

20.  Cotton. 

7.   Lead. 

21.  Glazed  porcelain. 

8.  Mercury. 

22.    Silk. 

9.   Carbon. 

23.    Bitumen. 

10.  Acids. 

24.   Sulphur. 

ii.   Aqueous  solutions  of  me- 

25.  Oxydi/ed  oils. 

tallic  salts. 

26.    Balata 

12.  Water. 

27.    India-rubber. 

13.  Wood  (moist). 

28.   Gutta-percha. 

14.  Earth  (moist). 

29.   Shellac. 

30.   Paraffin. 

31.   Hard  Rubber. 

32.   Glass. 

33-   Air. 

The  conducting  power  of  all  alloys  or  mixtures  of  different  metals 
is  very  much  less  than  that  of  any  one  of  the  metals  of  which  they 
are  composed.2  The  air  is  the  most  perfect  non-conductor  known, 
even  when  charged  to  saturation  with  aqueous  vapor,  but  it  should 
be  remarked  that  when  the  moisture  of  such  vapor  is  deposited 
upon  the  surface  of  insulating  supports,  it  may  form  a  conducting 
film  of  water. 

1170.  Specific  Resistance  of  Different  Metals.— The  re- 
sistance referred  to  in  (115^,  is  specific  resistance,  a  quality  which 
depends,  in  some  way  not  definitely  understood,  upon  the  internal 
molecular  structure  of  each  particular  substance.  Thus  an  iron  wire 
of  the  same  weight  and  thickness  as  the  copper  wire  used  in  the 
preceding  experiments  (in,  112)  would  offer  nearly  6  times  as  much 
resistance. 

If  the  resistance  of  a  pure  copper  wire  of  a  certain  length  and 
diameter  is  known,  the  resistance  of  other  wires,  of  similar  dimen- 
sions but  of  other  metals,  may  be  found  by  the  following  rule : 


For  Brass,  multiply  copper  resistance  by 
"     German-silver         "  "  " 

"     Iron  "  "  " 

Platinoid 
"     Platinum  "  "  " 


4-5 
12.9 

5-9 

19-5 
14.8 


»  For  Matthiessen's  determinations  of  the  specific  resistance  of  metals  and  alloys,  see 
SPRAGUE  :  Electricity,  etc.,  p.  282  ;  see  also  BENOTT:  Jour.  Soc.  Tel.  Eng.  iv.  112. 


58     Laws  and  Conditions  of  Electrical  Action. 

118.  Conditions  Affecting  Resistance. — In  the  case  of  a 
body  having  a  certain  specific  resistance,  the  actual  measurable  re- 
sistance depends  upon  certain  conditions,  viz. : 

(i)  Temperature. — The  resistance  of  all  metals  increases  with  the  tem- 
perature. The  converse  of  this  is  true  of  most  liquids  at  temperatures 
above  the  freezing  point  (162). 

(ii)  Length. — The  resistance  of  any  body  is  in  proportion  to  its  length, 
measured  in  the  direction  traversed  by  the  current. 

(iii)  Cross-section. — The  resistance  of  any  body  is  inversely  in  propor- 
tion to  its  area  of  its  cross-section.  Doubling  the  cross-section  halves  the 
resistance. 

Every  resistance  capable  of  being  measured,  must  necessarily  be 
equal  to  the  resistance  of  a  certain  length  of  a  standard  conductor  ; 
therefore  resistance  may  be  expressed  in  terms  of  length.  Thus  a  tele- 
graph line  made  up  of  two  or  more  sections  of  wire,  of  unequal 
thickness  or  gauge,  and  so  presenting  a  different  resistance  per  mile 
of  length,  may  be  expressed  in  terms  of  the  resistance  of  a  given 
length  of  a  standard  wire  :  that  is  to  say,  the  actual  resistance  of  any 
telegraph  line  must  represent  and  be  equal  to  the  resistance  of  a 
certain  length  of  wire  of  the  standard  gauge.  This  length  is  called 
the  reduced  length  of  the  line.  The  convenience  of  this  mode  of  re- 
ducing resistance  to  terms  of  length  in  making  tests  and  measure- 
ments of  lines  will  appear  hereafter. 

119.  Provisional  Theory   of  Electricity.— Before  under- 
taking to  analyze  and  explain  the  results  which  have  been  observed 
in  the  foregoing  experiments,  it  will  be  convenient  for  the  student  to 
form  some  sort  of  a  mental  conception  of  the  agency  which  produces 
the  phenomena  observed.     A  distinguished  electrical  engineer  has 
remarked : 

The  student  of  electricity,  in  considering  the  various  phenomena  which 
come  under  his  notice,  must  of  necessity  form  some  theory  in  his  mind  as 
to  the  nature  of  the  element  with  which  he  has  to  deal  ;  and  as  philosophers 
are  not  in  accord  as  to  its  nature  and  the  theory  of  its  action,  the  choice 
must  to  a  novice  be  a  difficult  one.  Without,  therefore,  in  the  least  offering 
any  opinion  on  this  point,  I  would  advise  him,  until  his  ideas  are  more 
matured,  to  regard  electricity  as  a  substance  like  water  or  gas,  having  a  ver- 
itable existence,  and  also  easily  converted  into  heat  and,  vice  versa,  in  other 
respects  indestructible.  LATIMER  CLARK:  Electrical  Measurement,  p.  vii. 

120.  Mechanical   Analogue   of  Electrical   Action.— Ac- 
cording to  this  manner  of  looking  at  the  question,  we  may  regard  a 
voltaic   cell   or  a  dynamo-electric  machine  as   a  sort  of  pump,  by 
which  positive  electricity  is  pumped  through  an  endless  channel  or 


Conception  of  Potential  and  Electromotive  Force.    59 

conduit,  as  water  might  be  pumped  through  a  pipe  to  the  top  of  a 
hill,  and  thence  allowed  to  flow  back  in  a  definite  channel  to  the 
foot  of  the  pump  from  whence  it  started.  This  illustration,  if  fixed 
in  the  mind,  will  materially  aid  the  student  in  forming  a  useful 
mental  conception  of  the  character  of  the  flow  of  electricity  in  a 
circuit  of  conductors. 

121.  Conception  of  Potential  and  Electromotive  Force. 
— When  water  is  pumped  to  an  elevation  by  the  application  of  power 
and  then  allowed  to  run  back  to  its  original  level,  it  is  capable  of  being 
made  to  do  work  in  the  course  of  its  descent  by  means  of  water-wheels 
or  otherwise,  and  it  is  obvious  that  the  amount  of  work  it  is  capable 
of  doing  under  these   conditions  depends  upon  three  things:     (i) 
the  height  of  the  fall,  (2)  the  quantity  of  water,  and  (3)  the  length 
of  time  the   effect  continues.     We   may  express  the   condition   of 
affairs  by  saying  that  the  water  which  has  been  raised  has  a  certain 
potential  energy \  which  may  be  defined  as  capacity  to  do  work,  and  for 
brevity  we  may  call  it  potential.     We  may,  therefore,  for  present  pur- 
poses, regard  electricity  as  a  material  fluid  to  which  a  certain  poten- 
tial has  been  given   by  the  action   of  a  battery  or  of  a  magneto- 
electric  machine   (80),   and  which  is   therefore   capable   of  doing 
mechanical  work,  as  is  the  case  with  the  descending  water.     That 
quality  of  a  voltaic  cell,  or  of  a  magneto  or  dynamo-electric  machine, 
by  virtue  of  which   it  confers  potential  upon  electricity  is  termed 
electromotive  force^  usually  abbreviated  to  e.  m.  f. 

122.  Practical  Electric  Units. — The  units  offeree  and  work, 
and  their  relation  to  force  of  gravitation,  have  already  been  referred 
to  (91),  and  it  has  also  been  explained  (94)  that  a  definite  quanti- 
tive  relation  exists  between  mechanical  force  and  the  force  of  an 
electric  current.     This  fact  enables  us  to  base  our  practical  units  of 
electrical  measurement  upon  absolute  units  ;  or  in  other  words,  our 
practical  units  are  derived  from  constants  furnished  by  nature.     The 
relation  or  law  connecting  the  two  forces  is  as  follows : 

The  force  which  a  given  current  traversing  a  circular  arc 
exercises  upon  a  magnetic  pole  of  given  strength  situated  at  its  center, 
is  equal  to  the  strength  of  the  pole  multiplied  by  the  strength  of  the 
current  and  also  by  the  length  of  the  arc,  and  divided  by  the  square 
of  the  radius  or  semi-diameter ;  that  is  to  say,  the  distance  from  the 
wire  from  the  magnet  pole. 

The  names  which  have  been  given  to  the  practical  electrical  units 
are  derived  from  the  names  of  philosophers  of  various  nationalities 
who  have  distinguished  themselves  by  electrical  discoveries  and 
investigations. 


60     Laws  and  Conditions  of  Electrical  Action. 

123.  The  Ampere. — The  unit  of  current  is  called  the  ampere.8 
It  is  equivalent  in  value  to  -fa  of  the  absolute  or  c.  g.  s.  unit  of  current 
(91).  The  actual  value  of  any  current  within  the  range  of  the  instru- 
ment may  be  determined  from  the  indications  of  a  properly  con- 
structed tangent  galvanometer.  This  is'  done  by  the  aid  of  the 
following  rules : 

(i;  Given  the  number  of  turns  and  the  mean  radius  of  the  coil  of  the  tangent 
galvanometer,  the  observed  deflection,  and  the  horizontal  force  of  the  earth's 
magnetism  at  the  place  of  observation  (94),  to  find  the  current  in  amperes: 

RULE. — Multiply  together  the  mean  radius  in  inches,  the  tangent  of  the  deflec- 
tion, the  horizontal  magnetic  intensity  of  ihe  earth  in  dynes,  and  the  reduction 
factor  4.0425,  and  divide  the  product  by  the  number  of  turns  in  the  coil.  The 
quotient  is  the  current  in  amperes. 

Example. — In  a  tangent  galvanometer  having  a  lo-in.  coil  wound  in  6  turns, 
and  giving  a  deflection  of  60°  in  Washington,  D.  C.,  in  1885,  required  the  value 
of  the  current. 

Ans.—  5  (in.)  X  1.732  (tan.  of  60°)  X  .2026  (dynes)  X  4.0425  (reduction 
factor)  -f-  6  (turns)  —  1.182  amperes.4 

(ii)  Given  the  number  of  turns  and  mean  radius  of  the  coil,  the  value  of  the 
current  and  the  horizontal  intensity,  to  find  the  deflection. 

RULE. — Multiply  together  the  number  of  amperes  and  the  number  of  turns,  and 
divide  this  product  by  the  product  of  the  mean  radius  in  inches,  the  horizontal  in- 
tensity in  dynes,  and  the  rednction  factor  4.0425.  The  quotient  will  be  the  t  ingcnt 
of  the  deflection. 

Example. — A  current  of  0.25  amperes  was  passed  through  the  coil  of  the  above 
described  galvanometer  in  New  York.  What  -was  the  deflection  ? 

Ans. — 0.25  (amperes)  X  6  (turns)  -*-  [5  (in.)  X  0.1872  (dynes)  X  4.0425 
(red.  fac.)]  in  0.3874  —  tangent  of  21°  nearly. 

*  AMPERE  (ANDRE  MARIE),  an  eminent  French  philosopher  and  mathematician,  in 
honor  of  whom  the  unit  of  current  received  its  name  ;  born  at  Lyons,  1775.  He 
became  inspector-general  of  the  university  (1808) ;  professor  in  the  Polytechnic  School 
(1809)  ;  and  Member  of  the  Institute  (1814).  Having'  made  important  discoveries  in 
electro-magnetism,  he  published  (1822)  his  Collection  of  Observations  on  Electro- 
Dynamics,  a  remarkable  work.  "  The  vast  field  of  physical  science,"  says  Arago, 
41  perhaps  never  presented  so  brilliant  a  discovery,  conceived,  verified,  and  completed 
with  such  rapidity."  He  subsequently  published  his  Theory  of  Electro- Dynamic 
Phenomena,  Deduced  from  Experiments  (1826).  Died  in  Marseilles,  1836. 

4  Each  unit  in  the  metric  system  has  its  decimal  multiples  and  sub-multiples  ;  that 
is  to  say,  measures  larger  or  smaller  than  the  standard  unit.  These  multiples  and 
sub-multiples  are  denoted  by  prefixes,  derived  from  the  Greek  and  Latin  languages 
respectively,  placed  before  the  names  of  the  units,  as  follows : 

PREFIX.  SIGNIFICATION.  |    PREFIX.  SIGNIFICATION. 

Micro- means  one  millionth  of  a .     !  Hecto- means  hundred  times  a . 

Milli-        "      one  thousandth  of  a .  Kilo-         "      thousand  times  a . 

Centi-       "      one  hundredth  of  a .  Myria-       "      ten  thousand  times  a . 

Deci-        "      one  tenth  of  a .  Mega-       "      one  million  times  a . 

Deka-       "      ten  times  a . 

Thus  a  millimetre  is  one-thousandth  of  a  metre ;  a  milliampere  is  one-thousandth 
of  an  ampere  ;  a  megohm  is  one  million  ohms,  etc.,  etc. 


Tkc  Coulomb. —  The  Volt. —  The  Ohm.          61 

(iii)  Example. — The  earth's  magnetism  in  Toronto,  Ont.,  being  the  direct- 
ing force  of  a  galvanometer  having  a  lo-in.  coil,  how  many  turns  must  be 
put  on  it  in  order  that  a  current  of  0.96  amperes  shall  give  a  deflection  of  60°  ? 

Ans. — 6  turns. 

From  the  above  explanations  and  examples,  it  will  he  seen  that  a 
standard  galvanometer  may  be  constructed,  from  which  it  is  always 
possible,  knowing  the  force  of  the  earth's  magnetism,  to  determine 
the  value  of  any  electric  current  in  amperes.  In  some  cases,  tangent 
galvanometers  are  graduated  so  that  the  amperes  may  be  read  di- 
rectly without  calculation.  Such  an  instrument  is  called  an  ampere- 
meter, or  more  commonly,  an  ammeter  (369). 

1233.  The  Coulomb. — The  quantity  of  current  which  traverses 
a  circuit  in  i  second,  when  the  strength  of  current  is  i  ampere,  is 
termed  a  Coulomb. f>  It  is  a  unit  which  is  of  little  or  no  practical 
utility  in  ordinary  telegraph  work,  or  in  fact  for  any  other  purpose, 
and  is  referred  to  here  only  because  it  has  been  given  a  place  in  the 
accepted  system  of  electric  units. 

124.  The  Volt. — The   unit  of  electromotive  force   is  called  the 
volt.6     It  closely  approximates  that  of  a  single  sulphate  of  copper 
or  gravity  cell  in  good  condition  (24),  so  that  in  telegraphic  work  it 
is  usually  accurate  enough  for  practical  purposes  to  estimate  i  cell 
equals  i  volt.      Accurately,  i  gravity  cell  has  an  e.  m.f.  of  1.07  volts. 
This  value  is  subject  to  slight  variation  from  various  causes.      It  is 
not  much  influenced  by  temperature  (153,  note). 

125.  The  Ohm. — The  unit  of  electrical  resistance  is  called  the 
ohm.7     It  is  equal  to  the  resistance  to  a  column  of  pure  mercury,  i 
sq.  millimetre  in  cross-section  and  106  centimetres  (more  or  less),  in 
length,8  at  a  temperature  of  o°  Centigrade  or  32°  Fahrenheit. 

5  COULOMB  (CHARLES  AUGUSTIN  DE),    a   distinguished   mathematician,  born  at 
Angouleme,  France,  1736.     He  is  regarded  as  the  founder  of  experimental  physics  in 
France.     The  theory  of  electricity  is  largely  indebted  to  the  investigations  of  this  phi- 
losopher.    Died,  1806. 

6  VOLTA  (ALESSANDRO),  born  at  Como,  Italy,  1745 ;  was  first  professor  of  physics 
at  Como,  and  afterward  in  the  University  of  Pavia,  where  he  taught  and  studied  for 
30  years.     In  1782,  he  invented  the  electrical  condenser  (317),  and  finally  arrived  at 
the  invention  of  the  famous  cell  which  bears  his  name  (8),  which  he  described  in  a  let- 
ter to  Sir  Joseph  Banks  in  1800.     Summoned  to  Paris  by  Napoleon,  he  received  the 
gold  medal  of  the  Institute,  of  which  he  became  a  member  in  1802.     His  works  were 
published  in  9  volumes,  in  Florence,  in  1816.     Died,  1827. 

7  OHM  (GEORG  SIMON),  born  at  Erlangen,  Bavaria,  1787  ;  studied  in  his  native 
city ;  was  appointed  (1817)  professor  of  physics  at  the  Jesuit  college  of  Cologne,  di- 
rector of  Polytechnic  School  at  Nuremburg  (1883),  and  professor  (1849)  at  Munich, 
where  he  died  in  1874.     He  discovered  the  so-called  Ohm's  law  (124),  which  he  pub- 
lished in  1827,  and  for  which  was  awarded  the  Copley  medal  by  the  Royal  Society  of 
London. 

•  In  1861,  the  British  Association  for  the  Advancement  of  Science,  at  the  suggestion 


62      Laws  and  Conditions  of  Electrical  Action. 

The  resistances  of  various  wires  used  as  telegraphic  conductors  is 
given  in  the  tables,  pp.  94,  112. 

126.  Resistance  of  Liquids. — The  resistance  of  liquids  is 
enormously  greater  than  that  of  metallic  substances.  The  relative 
specific  resistances  of  some  of  the  voltaic  solutions  used  in  telegraphy 
are  as  follows  : 9 

Pure  copper  (standard  of  comparison) i. 

Pure  rain  water 40,653,723. 

Water  12  parts,  sulphuric  acid  i  part 1,305,467. 

Sulphate  of  copper  i  Ib. ,  water  i  gallon 18,450,000. 

Saturated  solution  sulphate  of  zinc 17,330,000. 

Table  iv,  on  the  next  page,  contains  the  results  of  more  recent 
determinations  of  the  specific  resistance  of  copper  and  zinc  solutions 
at  various  temperatures,  computed  from  the  experiments  of  Becker.10 
As  the  temperature  rises,  the  resistance  falls  off.  This  effect  is  fur- 
ther referred  to  in  (164). 

of  Sir  William  Thomson,  appointed  a  committee  on  electrical  standards,  which,  after 
a  long  series  of  experiments  by  eminent  physicists,  determined  the  value  of  the  ohm  to 
be  nearly  that  of  a  column  of  pure  mercury  105  centimetres  long  and  i  square  millim- 
etre in  cross-section,  at  temp.  o°  centigrade,  and  officially  caused  resistance  coils  made 
of  wire  of  an  alloy  of  platinum  and  silver  to  be  issued  as  standards.  Resistance  coils 
copied  from  these  standards  are  known  as  B.  A.  units  or  ohms.  More  recent  careful 
determinations  of  Lord  Rayleigh  and  many  others  have  proved  beyond  doubt  that  the 
B.  A.  unit  or  ohm  is  more  than  i  per  cent,  too  small.  An  attempt  has  accordingly 
been  made  to  substitute  for  the  old  standards  new  ones  of  the  corrected  value.  In  ac- 
cordance with  the  recommendation  of  the  International  Congress  of  Electricians,  held 
in  Paris  in  1884,  a  legal  ohm  is  denned  to  be  a  mercury  column  of  the  above  section, 
and  106  cm.  in  length.  The  exact  ratio  is : 

i  Legal  ohm  =  1.0112  B.  A.  ohm. 
i  B.  A.  ohm  =  0.9889  legal  ohm. 

At  the  meeting  of  the  British  Association  in  September,  1890,  it  was  recommended 
that  the  value  for  the  mercury  column  of  106.3  cm-  be  substituted  for  the  106  cm.  of 
the  International  Congress,  and  it  is  not  unlikely  that  this  value  may  ultimately  be 
adopted. 

In  Germany,  the  Siemens  unit  (known  as  the  S.  U.)  is  largely  used,  and  many  of 
the  older  instruments  now  in  use  in  the  United  States  are  adjusted  to  this  standard. 
It  is  designed  to  be  equal  to  a  column  of  mercury  i  metre  long  and  i  sq.  mm.  cross- 
section  at  temp.  o°  C. 

i  Siemens  unit  =  0.9540  B.  A.  ohm. 
i  B.  A.  ohm.     =  1.0486  S.  U. 

»  MOSES  G.  FARMER  :  Shaffner's  Telegraph  Manual,  514. 

10  F.  JENKIN  :  Electricity  and  Magnetism,  259.  The  maximum  conductivity  of  s.  z. 
solution  is  23.5  per  cent  (s.  g.  1.286)  according  to  KOHLRAUSCH  :  Physical  Measure- 
ment, p.  326.  For  other  tables  of  resistances  of  liquids,  see  SPRAGUE  :  Electricity,  etc. 
(2d  ed.),  298;  STEWART  and  GEE:  Elementary  Practical  Physics,  219;  NIAUDET  : 
Electric  Batteries  (Fishback's  Translation),  255  ;  PRESCOTT  :  Electricity  and  Elec. 
Tel.,  182.  For  method  of  measurement  see  F.  KOHLRAUSCH  :  Jour.  Soc.  Tel.  Eng. 
xiii,  290. 


Ohms  Law. 


TABLE   IV. 

SPECIFIC  RESISTANCES  OF  VOLTAIC  SOLUTIONS. 
SULPHATE   OF   COPPER. 


Percentage 
of  salt  in 
Solution. 

14° 

16° 

18° 

20° 

24° 

28° 

30° 

Centigrade. 

8 

12 

16 

45-7 
36.3 
31.2 

43-7 
34-9 
30.0 

41.9 

33-5 
28.9 

40.2 
32.2 
27.9 

37-1 
29.9 
26.1 

34-2 
27.9 
24.6 

32.9 
27.0 
24.0 

Resistance  of 
i   cubic   centi- 

20 
24 

28 

28.5 
26.9 
24-7 

27.5 
25-9 
23-4 

26.5 
24.8 

22.1 

25.6 
23-9 

21.0 

24.1 

22.2 

18.8 

22.7 
20.7 
16.9 

22.2 
2O.  O 

16.0 

metre  ex- 
pressed in 
ohms. 

SULPHATE    OF    ZINC. 


10°         12° 

14°      16° 

18° 

20° 

22° 

24°           Centigrade. 

96  grams   in   100  \ 
c.  c.  of  solution.  ) 

22.7 

21.4 

20.2 

19.2 

18.1 

I7.I 

I6.3 

!  Resistance  of  i 

cubic  centi- 

Same    solution  \ 

metre  expressed 

with    an     equal  > 

21.  1 

20.3  19.5 

18.8 

18.1 

r7-3.         in  ohms. 

volume  of  water.  ) 

i 

127.  Ohm's  Law. — The  fundamental  relation  which  exists  in 
every  electric  circuit  between  electromotive    force,    resistance  and 
current,  is  expressed  by  Ohm's  law,  which  may  be  formulated  in  the 
following  propositions  : 

(i)  In  any  electric  circuit,  the  current  is  the  quotient  of  the  electromotive 
force  divided  by  the  resistance  ;  hence  the  current  in  amperes  maybe  found 
by  dividing  the  e.  m.  f.  in  volts  by  the  resistance  in  ohms. 

(ii)  In  any  electric  circuit,  the  electromotive  force  is  the  product  of  the 
current  and  the  resistance  ;  hence  the  total  e.  m.  f.  in  volts  may  be  found  by 
multiplying  together  the  current  in  amperes  and  the  resistance  in  ohms. 

(iii)  In  any  electric  circuit,  the  resistance  is  the  quotient  of  the  electro- 
motive force  divided  by  the  current ;  hence  the  resistance  in  ohms  may  be 
found  by  dividing  the  e.  m.  f.  in  volts  by  the  current  in  amperes. 

128.  Joule's  Law.11 — The  relation  which  exists  between   cur- 
rent and  mechanical  work  is  expressed  by  Joule's  law,  which  may 
be  formulated  in  the  following  propositions : 

11  JOULE  (JAMES  PRESCOTT),  born  in  Salford,  England,  1818.  A  self-taught  philos- 
opher, distinguished  for  the  extent,  originality,  and  accuracy  of  his  physical  researches. 
He  ascertained  in  1841,  the  law  of  the  evolution  of  heat  by  the  electric  current  (128), 
and  determined  in  1850,  the  numerical  ratio  of  equivalency  between  heat  and  mechan- 
ical force  (92).  His  discoveries,  which  are  too  numerous  to  permit  more  than  general 


64     Laws  and  Conditions  oj  Electrical  Action. 


(iv)  In  any  electric  circuit,  the  rate  of  doing  worK  is  the  product  of  the 
e.  m.  f.  and  the  current  ;  hence  the  rate  in  which  work  is  being  done  in 
watts  (150)  may  be  found  by  multiplying  together  the  e.  m.f.  in  volts  and  the 
current  in  amperes. 

(v)  In  any  electric  circuit,  the  rate  of  doing  work  is  the  product  of  the 
current  multiplied  into  itself  and  into  the  resistance  ;  hence  rate  of  working 
in  watts  may  also  be  found  by  multiplying  together  the  resistance  and  the 
square  of  the  current  in  amperes. 

129.  The   term   work,   as  herein  used,  includes   the  work  which 
appears  in  the  form  of  heat,  as  well  as  that  which  produces  physical 
motion. 

130.  Experimental  Proof  of  Ohm's  Law. — The  student  is 
now  prepared   to  understand   an  explanation    of  the   results  which 

have  been  referred  to  in  the 
preceding  paragraphs  (108 — 
113).  Referring  to  the  dia- 
gram, Fig.  49,  we  may  trace 
the  circuit  as  follows  :  Begin- 
ning at  the  copper  or  the  posi- 
tive pole  of  the  battery,  thence 
through  the  62  feet  of  copper 
wire  which  forms  the  coil  of 
the  galvanometer  ;  thence  to 
the  zinc  Z  or  negative  pole  of 
the  battery ;  thence  in  succes- 
sion through  the  s.  z.  solution 
and  the  s.  c.  solution  S  to  the 
copper  plate  C  of  the  first  cell ; 
thence  to  the  zinc  plate  Z  of 
the  next  cell,  and  through  the 

solution  to  the  copper,  and  so  on  through  the  series  until  the  starting 
point,  the  copper  plate  of  the  terminal  cell,  is  reached. 

131.  Internal  Resistance  of  the  Cell. — The  solution  in  each 
cell  may  be  regarded  as  a  liquid  conductor  of  cylindrical  form,  having 
a  length  of  about  3  in.  (the  average  distance  between  the  copper  and 
zinc  plates)  and  a  cross-section  of  about  28  sq.  in.     When  a  cell  is 
in  good  working  condition,  the  resistance  of  the  contained  liquids,  at 
ordinary  temperatures,  is  about   4  ohms,  and  may  be  regarded  as 

mention  here,  have  been  intimately  related  to  the  remarkable  theory  of  the  correlation 
of  the  physical  forces  (p.  38,  note  8)  which  was  developed  by  Mayer,  Helmholtz,  Seguin, 
Faraday,  and  Grove.  His  researches  in  electro-magnetism,  particularly  in  respect  to 
its  application  as  a  motive  power,  were  extensive  and  important.  Honors  were  con- 
ferred on  him  by  almost  every  learned  society  in  the  world.  His  scientific  papers  were 
collected  and  published  by  the  Physical  Society  of  London  in  1884.  Died  1889. 


FIG.  49,     Diagram  of  Galvanometer  and  Battery 
Circuit. 


Kic.  50.     Cells  in  Series  with 
Galvanometer. 


Internal  Resistance  of  t/ic   Cell. — First  Case.      65 

approximately  equivalent  to  that  of  250  feet  of  copper  wire  of  the 
thickness  of  that  in  the  coil  of  our  galvanometer  (103).  The  actual 
resistance  of  the  zinc  and  copper  plates  of  each  cell,  being  at  most 
but  an  insignificant  fraction  of  i  ohm,  may  in  the  present  instance 
be  disregarded  in  our  computations. 

132.  First  Case. — In  the  first  ex- 
ample, we  begin  with  4  cells  in  circuit  in 
a  single  series,  as  shown  in  Fig.  50. 

This  figure  is  a  diagrammatical  or  con- 
ventional illustration  of  precisely  the  same     i 
thing  which   is  shown   in   Fig.   46.      The    I 
zinc  plate  of  each  cell  is  represented  by  a 
thick  black  line,  and  the  copper  by  a  thin 
line.     The    symbol  for  the  galvanometer 
explains  itself.      In   like  manner,   Fig.  51 
corresponds  to  Fig.  47,  and  Fig.  52  to  Fig. 
48.     In  Figs.  51   and  52,  a  black  dot  at 

the  intersection  of  two  wires  indicates  that  they  are  electrically 
united  at  the  junction.  This  conventional  representation  of  batteries, 
galvanometers,  circuits,  and  other  appliances  will  be  employed  here- 
after in  this  work  (208). 

In  this  case,  each  cell  has  an  approximate  e.  m.f.  of  i  volt  (124), 
this  value  depending  not  at  all  upon  the  size  of  the  element,  but 
solely  upon  its  chemical  constitution.  The  aggregate  £.;#*./]  of  the 
4  cells  of  the  series  is  therefore  4  volts.  The  aggregate  resistance 
of  the  4  cells  is  16  ohms,  and  that  of  the  galvanometer  r  ohm.  We 
may  neglect  also  the  inappreciable  resistance  of  the  short  connecting 
wires  between  the  battery  and  the  galvanometer,  and  call  the  sum 
of  the  resistances  in  the  circuit  (battery  and  galvanometer)  17  ohms. 
By  Ohm's  law  (127, i),  we  divide  the  e.  m.f.  4  (volts)  by  the  resist- 
ance 17  (ohms),  and  our  quotient  is  0.235  (amperes). 

With  3  cells  in  -like  manner,  we  have  an  e.  m.f.  of  3  volts,  an 
aggregate  resistance  of  13  ohms,  and  by  Ohm's  law  a  current  of 
0.230  amperes;  and  so  in  the  remaining  cases.  Continuing  this 
method  of  procedure,  we  get  results  which  may  be  tabulated  as 
follows : 


Cells  in  Series. 

Deflections. 

Tangents. 

E.  M.  F. 

Resistance. 

Current. 

4 

58° 

1.  60 

4 

•17 

0-235 

3 

57i° 

l.56 

3 

•13 

0.230 

2 

5<*° 

1-50 

2 

•9 

0.222 

I 

53T 

i-35 

I 

•5 

O.2OO 

66      Laws  and  Conditions  of  Electrical  Action. 

We  find,  therefore,  that  the  tangents  of  the  angles  of  deflection  are 
in  proportion  to  the  strength  of  the  current  in  amperes,  as  computed 
by  Ohm's  law  from  known  electromotive  forces  and  known  resistances. 

133.  Second  Case.— Take 
the  next  arrangement  (109),  in 
which  we  have  2  series  of  cells 
and  2  cells  in  each  series,  Fig. 
51.  The  question  now  arises: 
If  the  resistance  of  each  cell  is 
4  ohms,  what  will  be  the  resist- 
ance of  the  group?  It  is  less 
than  in  the  preceding  case,  as 
Fig.  51.  Cells  in  Parallel  Series  with  Gal-  the  increased  deflection  of  the 

vanometer.  ji          i  i  •    i 

needle    shows,    and    as    might 

have  been  inferred  from  the  fact  that  the  current  from  each  series  of 
cells  does  not  now  pass  through  the  other  series,  nor  encounter  its 
resistance.  Neither  is  the  e.  m.f.  of  one  series  superimposed  upon 
that  of  the  other  series  as  before.  A  little  reflection  will  make  it 
clear  that  the  present  arrangement  is  precisely  equivalent  to  2  cells 
in  series,  each  having  copper  and  zinc  plates  of  double  the  original 
area.  Hence  we  may  consider  the  cross-section  of  the  liquid  con- 
ductor to  be  doubled,  while  its  length  remains  unaltered,  from  which 
it  follows  that  its  resistance  is  but  half  what  it  was  originally  (118). 
134.  Law  of  Joint  Resistances.— The  law  determining  the 
resistance  of  any  circuit  which  divides  into  two  or  more  branches 
which  reunite  at  another  point,  is  a  general  one,  and  applicable  in 
all  such  cases,  whether  of  batteries  or  of  conductors.  The  resist- 
ance offered  by  two  or  more  such  branches  is  termed  their  joint 
resistance,  and  is  computed  by  the  following  rules : 

RULE  i. — Add  together  the  reciprocals  of  the  individual  resistances  of  all 
the  branches,  and  the  reciprocal  of  the  result  will  be  the  joint  resistance  of  tJie 
group. 

The  reciprocal  of  any  number  is  the  fraction  obtained  by  dividing 
unity  (or  i)  by  that  number;  and  the  reciprocal  of  any  common 
fraction,  is  that  fraction  itself  inverted.  Thus  the  reciprocal  of  2  is 
\  or  0.5  ;  and  conversely,  the  reciprocal  of  0.5  or  \  is  2.  The  recip- 
rocal of  J  is  f .  A  table  of  reciprocals  is  given  on  page  67. 

In  case  there  are  only  two  branches,  a  simpler  method  of  compu- 
tation may  be  used : 

RULE  2. — Multiply  together  the  individual  resistances  of  the  two  branches, 
and  divide  the  product  by  their  sum  ;  the  quotient  will  be  the  joint  resistance. 


Table  of  Reciprocals. 


TABLE     V. 
RECIPROCALS    OF    NUMBERS    FROM    1    TO    100. 


No. 

Rec. 

No.    Rec. 

No. 

Rec. 

No. 

Rec. 

No. 

Rec. 

I 

1.  000 

21    .0467 

41 

.0244 

61 

.0164 

81 

.0123 

2 

.5000 

22    .0454 

42 

.0238 

62 

.0161 

82 

.0122 

3 

•3333 

23 

•0434 

43 

.0232 

63 

.0159 

83 

.0120 

*!• 

.2500 

24 

.0416 

44 

.0227 

64 

.0156 

84 

.0119 

5 

.2000 

25 

.0400 

.45 

.0222 

65 

.0154 

85 

.0118 

6 

.1667 

26 

.0385 

46 

.0217 

66 

.0151 

86 

.0116 

7 

.1428 

27 

.0370 

47 

.0213 

67 

.0149 

87 

.0115 

8 

.1250 

28 

•0357 

48 

.0208 

68 

.0147 

88 

.0114 

9 

.mi 

29 

•0344 

49 

.O2O4 

69 

.1045 

89 

.OII2 

10 

.1000 

30 

•0333 

50 

.0200 

70 

.0143 

9° 

.OIII 

n 

.0909 

31 

.0323 

5i 

.0196 

7i 

.0141 

91 

.OIIO 

12 

.0833 

32 

.0312 

52 

.0192 

72 

.0139 

92 

.0108 

13 

.0769 

33 

.0303 

53 

.0188 

73 

.0137 

93 

.0107 

14 

.0714 

34 

.0294 

54 

.0185 

74 

•0135 

94 

.0106 

15 

.0667 

35 

.0286 

55 

.0182 

75 

•0133 

95 

.0105 

16 

.0625 

36 

.0277 

56 

.0178 

76 

.0131 

96 

.0104 

17 

.0588 

37 

.0270 

57 

•0175 

77 

.0130 

97 

.0103 

18 

•0555 

33 

.0263 

53 

.OI72 

78 

.0128 

98 

.0102 

19 

.0526 

39 

.0256 

59 

.0169 

79 

.0126 

99 

.0101 

20 

.0500 

40 

.0250 

60 

.0166 

80 

.0125 

100 

.0100 

Any  sum  multiplied  by  the  reciprocal  of  a  number  is  equal  to  the  same 
sum  divided  by  the  number  corresponding  to  the  reciprocal.  In  the  table, 
the  reciprocals  are  those  of  whole  numbers,  but  it  is  easy  to  extend  their 
use  to  decimals,  or  to  mixed  numbers,  by  shifting  the  decimal  point  ;  thus, 
the 

Reciprocal  of  390  =  .00256 

"     39  =  -0256 

3-9  =  -256 

•39  2.56 

"  "         .039  25.6 


68      Lazi's  and  Conditions  of  Electrical  Action. 


135.  In  the  present  case  we  have  2  branches,  with' a  resistance  of 
8  ohms  in  each  branch.  Hence  we  have  8x8  =  64;  8  +  8=  16; 
64  -^-  1 6  =  4  ;  add  galvanometer  i,  and  we  have  as  total  resistance 
5.  Dividing  the  e.  m.f.,  2,  by  this  amount  gives  a  current  of  0.4 
amperes.  We  have  therefore : 


Cells  in  parallel  series. 

Deflection.       Tangent. 

E.  M.  F. 

2 

Resistance. 

Current. 

4 

6gf°               2.70 

5 

0.4 

136.  Third  Case. — Next  we  have  (no)  the 
4  copper  terminals  connected  to  one  terminal  of 
the  galvanometer  and  the  4  zincs  to  the  other 
terminal,  as  in  Fig.  52.  In  this  case,  by  the  rule 
(134),  the  reciprocal  of  4  is  0.25  ;  the  sum  of  the 
four  reciprocals  is  therefore  i,  the  reciprocal  of 
which  is  i,  and  this  added  to  the  galvanometer 
resistance  i,  makes  a  total  of  2,  while  the  e.  m.  f. 
is  now  reduced  to  i.  Hence,  we  have  in  this 
case: 


Cells  in  .  j)enection.    Tangent.   E.  M.  F. 

Resistance.!  Current. 

« 

73i            3-38             i 

2            |      0.5 

ohms. 


•— '  137.  Passing  next  to  the  experiment  in  (108), 

in  which  we  found  that  having  3  cells  in  circuit 
with  the  galvanometer,  and  300  feet  of  a  certain 
gauge  copper  wire,  the  deflection  apparently  in- 
dicated that  we  produced  exactly  the  same  current 
in  the  circuit  that  we  did  with  i  cell  when  the  cop- 
per wire  was  not  included.  Let  us  see  whether 
Ohm's  law  accounts  for  the  result.  We  find  from 
the  copper  wire  table  (p.  94)  that  the  resistance 
of  the  length  of  wire  included  is  approximately  2 

We  have,  therefore  : 


Fig.  52.  Cells  in  Par- 
allel with  Galva- 
nometer. 


Resistance  of  3  cells  battery ; 12  ohms. 

"  "   galvanometer i        " 

"  "   300  feet  copper  wire 2 

Total 15  ohms. 

3  (volts)  -T-  15  (ohms)  =  0.2  (amperes). 


Branch  or  Derived  Circuits,  69 

In  the  other  case  we  had  : 

Resistance  of  i  cell 4  ohms. 

"   galvanometer i       " 


Total 5  ohms. 

i  (volt)  -5-  5  (ohms)  —  0.2  (amperes). 

138.  Ohm's  law  is  therefore  confirmed  in  every  particular  by  the 
results  of  experiment,  and  observation,  and  we  learn,  moreover,  the 
important  fact  that  the  quantity  of  current  traversing  any  given  circuit 
may  be  varied  either  by  varying  the  electromotive  force  or  by  varying 
the  resistance. 

139.  We  also    learn  from  Ohm's   law,  as  interpreted  by  the  ex- 
periments which  have  been  made,  that  every  portion  of  an  undivided 
or  non-branching  circuit  is  traversed  by  the  same  quantity,  or  number  of 
amperes^  of  current  at  the  same  time,  without  reference  to  its  relative 
resistance. 

140.  Currents  in  Branch  Circuits.— When  any  circuit  divides 
into  two  or  more  branches  a  current  traversing  that  circuit    dis- 
tributes itself  between    these  branches  inversely  in    proportion    to 
their  respective  resistances,  or,  what  is  the  same  thing,  directly  in 
proportion  to  their  several  conductivities.     The  branches  are  also 
termed  shunts  or  derived  circuits.       Each    such   branch  may  be  re- 
garded as  a  shunt  to  all  the  other  branches  in  parallel  with  it. 

The  word  shunt  is  of  English  origin,  and  is  derived  from  the 
analogy  of  a  railroad  siding  where  trains  pass  each  other,  which  in 
that  country  is  known  as  a  shunt. 

141.  Electric  Potential. — Having  thus    gained    some    experi- 
mental as  well  as  theoretical  knowledge  of  electromotive  force  (121), 
resistance  (115),  and  current  (91),  the  student  should  next  endeavor 
to  acquire   a  definite    understanding   of  the   meaning  of  the  term 
potential.     The  resemblance  between  the  behavior  of  electricity  and 
that  of  a  material  fluid  like  water  has  already  been  pointed  out  (120). 
Recurring  to  this  analogy,  if  we  assume  a  stream  of  water  to  be 
flowing   through  a  closed  pipe,  we  know  that  as  soon  as  the  flow 
has   become    steady,    exactly  the    same     number    of    gallons    per 
minute  will  pass  through  every  cross-section  of  the  pipe,  whatever 
may  be  the  difference  in  its  diameter  at  different  points.     This  is 
exactly  analogous  to  that  which  occurs  in  the  case  of  an  electric 
current  (139)- 

142.  Although  the  quantity  of  water  which   passes   must  neces- 
sarily be  the  same  in  every  cross-section  of  the  pipe,  the  pressure 


place  in  the  electric  conductor. 


FIG.  53.    Hydraulic  Illustration  of  Electric 
Potential. 


70      Laws  and  Conditions  of  Electrical  Action. 

per  square  inch  is  by  no  means  equal  throughout,  and  this  is  true 
whether  the  pipe  is  level  and  whether  it  is  of  uniform  diameter  or 
otherwise.  As  we  proceed  along  a  horizontal  pipe  in  the  direction 
of  the  flow,  we  observe  the  pressure  becomes  less  and  less  as  we  go 
farther  away  from  the  supplying  reservoir. 

143.  Illustration  of  Fall  of  Potential. — A  like  effect  takes 

A  fall,  technically  termed  a  drop  in 
potential,  occurs  as  we  recede 
from  the  source  of  electricity, 
just  as  there  is  a  fall  of  pressure 
in  the  water-pipe.  For  example, 
let  Fig.  53  represent  a  vessel 
~  filled  with  water.12  The  tap  at  C 
is  closed,  and  the  water  stands 
at  the  same  level  in  all  the  verti- 
cal tubes,  showing  that  no  differ- 
ence of  pressure  exists,  and 

consequently  there  can  be  no  current  of  flow  in  the    liquid.     But 
when  the  tap  at  C  is  opened,  as  in  Fig.  54,  it  will  be  observed  that 
the  level  in  the  several  vertical  tubes  stands  lower  and  lower  as  we 
pass    from    A    toward    C.     The 
height  of  water  in  each  tube  in- 
dicates the  pressure  which  exists 
at  the  point  of  its  junction  with 
the  tube  B.     This  difference  in 
hydrostatic  pressure  between  dif- 
ferent points  in  the  pipe  produces 
the  flow  of  water  which  we  call  a 
current.     The  original  cause  of 
the  flow  is  manifestly  the  force 

which  lifted  the  water  in  the  first  place  to  a  point  above  the  level  of 
the  pipe  B,  and  thus  conferred  upon  it  the  pressure  or  potential 
which  it  now  has  (121).  Therefore  we  may  say  without  error,  that 
electromotive  force  causes  potential  to  exist.  When  resistance  is  re- 
moved, a  fall  of  potential  occurs  at  some  point,  and  this  fall  of  poten- 
tial gives  rise  to  an  electric  current.  Therefore  the  fact  of  the  exist- 
ence of  an  electric  current  is  conclusive  evidence  of  the  existence  of 
a  difference  of  potential  between  two  different  points  in  the  circuit 
through  which  the  current  flows. 

1S  This  excellent  illustration  is  from  Professor  ELROY  M.  AVERY'S  Elements  of  Natu- 
ral Philosophy,  of  which  the  chapter  on  electricity  and  magnetism  has  been  separately 
published  by  Sheldon  &  Co.,  New  York. 


FIG. 


Hydraulic  Illustration  of  Uniform 
Fall  of  Potential. 


Graphic  Illustration  of  the  Electric  Circuit.     71 


FIG.  55.     Hydraulic   Illustration  of  Varying 
Fall  of  Potential. 


144.  Fall  of  Potential  Proportionate  to  Resistance.— 

The  fall  of  potential  between  any  two  points  in  a  circuit  bears  the 
same  ratio  to  the  fall  of  potential  in  the  whole  circuit  that  the 
resistance  between  those  points 
does  to  the  total  resistance  of  the 
circuit.  In  other  words,  in  the 
whole  or  any  portion  of  a  circuit, 
the  fall  of  potential  is  always  in 
proportion  to  the  resistance.  In 
Fig.  55,  the  horizontal  pipe  is  in 
two  portions  of  different  diame- 
ters, and  in  this  case  it  will  be 
observed  that  the  fall  of  the 
pressure  is  more  rapid  along  the  smaller  than  along  the  larger  section. 

145.  Graphic  Illustration  of  the  Electric  Circuit. — We  may 
represent  by  a  diagram  all  the  essential  characteristics  of  the  electric 
circuit  in  a  manner  first  pointed  out  by  Ohm  in  1828.     For  example. 

let  the  ring  in  Fig.  56  represent  a  conductor  of 
uniform  resistance  having  a  source  of  electricity  at 
the  point  A.  The  electricity  from  this  point  will 
be  diffused  over  both  halves  of  the  ring;  the  posi- 
tive going  toward  a  and  the  negative  toward  b, 
both  uniting  at  c.  As  the  conductor  is  assumed  to 
be  homogeneous,  it  follows  that  equal  quantities  of 
electricity  traverse  all  sections  of  the  ring  at  the 
Fig.  56.  Geometrical  same  time  (139).  If  we  assume  that  the  flow  of 
illustration  of  Ohm's  the  current  from  one  crOss-section  of  the  ring  to 

another  is  due  to  the  difference  of  potential  which 
exists  between  the  two  points  (143),  and  that  the  quantity  which 
passes  is  proportional  to  this  difference  of  potential  (144),  it  follows 
that  the  positive  and  negative  currents,  proceeding  in  opposite  direc- 
tions from  A,  must  exhibit  a  decrease  in  potential  the  farther  they 
recede  from  the  starting  point.  This  decrease  in  potential  may  be 
graphically  represented  in  a  diagram,  the 
analogy  of  which  to  the  hydraulic  ap- 
paratus of  Fig.  54  will  be  apparent  upon 
inspection  and  comparison.  Suppose  the 
ring  of  Fig.  56  to  be  stretched  out  in  a 
straight  line  A  A',  Fig.  57.  Let  the 
vertical  line  A  B  (technically  termed  an 
ordinate)  represent  the  positive  potential 
at  A,  and  A'  B'  in  like  manner  the  nega- 


B 


B 


Fig.  57.    Illustration  of  Uniform 
Fall  of  Potential. 


/  2      Laws  and  Conditions  of  Electrical  Action. 

tive  potential  at  A';  then  the  line  B  B'  will  denote  the  value  of  the 
potential  in  all  parts  of  the  circuit  by  the  correspondingly  varying 
lengths  of  the  vertical  ordinates  at  any  point  between  Kc  or  c  A'. 
The  quantity  of  the  current  is  proportional  to  the  steepness  of  the 
fall.  This  may  be  considered  also  as  a  graphic  representation  of 
Ohm's  law  (127). 

146.  Fall  of  Potential  in  a  Non-homogeneous  Circuit. — 
In  practice,  in  the  circuits  employed  in  telegraphy,  the  conductor  is 
never  homogeneous,  but,  like  the  water-pipe  referred  to  in  (144),  is 

made  up  of  several  conductors  of  varying 
conductivity.  To  illustrate  this  condition 
of  things  in  a  diagrammatic  form,  let  the 
conductor  A  A',  Fig.  58,  consist  of  two 
portions  having  respectively  different 
cross-sections.  If  we  assume  the  cross- 
.  section  of  A  //,  for  example,  to  be  greater 

than  that  of //A'  in  the  proportion  of  •*  to 
Fig.  58.    Illustration  of  Variable  .*.  ,°. 

Fall  of  Potential.  2;  then  if  equal  quantities  of  electricity 

pass  through  all  sections  in  equal  times, 

as  stated  in  (139)  and  (141),  the  difference  of  potential  between 
the  extremities  of  the  thicker  wire  will  be  only  two  thirds  what  it 
would  be  in  the  case  of  the  thinner  wire  of  equal  length.  Hence, 
the  fall  or  drop  in  potential  will  be  less  in  the  thick  than  in  the  thin 
wire,  as  shown  by  the  line  Br,  in  Fig.  58.  The  greater  therefore  the 
resistance  of  the  conductor,  the  greater  the  fall  of  potential.  This 
result  is  expressed  in  the  following  law : 

In  any  electric  circuit,  the  fall  of  potential  is  directly  as  the  specific 
resistances  (117)  of  the  sei'eral  conductors  composing  it,  and  inversely  as 
the  area  of  their  cross-sections. 

The  simplest  circuit,  therefore,  when  laid  out  in  diagrammatic 
form,  exhibits  a  series  of  gradients  expressing  the  potential  of  its 
various  parts. 

147.  Electrostatic    Capacity. — A    body  charged  with   elec- 
tricity in  a  static  condition,  as,  for  example,  a  long  submarine  cable, 
a  condenser  (317)  or  the  well-known  apparatus  called  the  Leyden 
jar,  is  said  to  be  in  a  state  of  electrification.     This  effect  is  also  ob- 
servable upon  well-insulated  land  lines  of  considerable  length,  and 
is  one  which  in  certain  special   methods  of  telegraphy  needs  to  be 
taken  into  consideration,  as  will  hereafter  appear.     The  quantity  of 
static  electricity  (82)  thus  held  by  any  conductor,  or  that  which  any 
body  is  capable  of  containing,  is  termed  its  capacity.     This  is  often 
called  also  electrostatic  capacity  and  inductive  capacity. 


The  Watt. 


73 


148.  The  Farad. — The  unit  of  capacity  is  called  \hzfarad,™  but 
the  capacities  required  to  be  measured   in  telegraphy  being  usually 
very  small,  they  are  more  conveniently  expressed  in  micro-farads  (p.  60, 
note  4).      Further  explanation  of  this  subject   is  reserved  until  the 
effects  of  static  electricity  upon  telegraph  lines  require  consideration. 

149.  Power,  or  Rate  of  Work. — It  has  been  stated  elsewhere 
(92)  that  every  electric  current  is  capable  of  doing  a  certain  amount 
of  work.      This  definite  amount  of  work  may,  however,  obviously  be 
done  in  a  greater  or  less  length  of  time,  that  is  to  say,  at  a  different 
rate,  and  this  rate  of  work  is  called  power. 

150.  The  Watt. — The  electric  unit  of  power,  or  rate  of  working, 
is  called  the  watt.^     It  equals  i  volt  multiplied  by  i  ampere,  or  7J^ 
of  a  mechanical  horse-power.      In  any  circuit  the  power  equals  the 
square  of  the  current  in  amperes  multiplied  into  the  resistance  in  ohms. 

TABLE     VI. 
SYNOPSIS  OF   PRACTICAL  UNITS.15 


1 

Value. 

Unit. 

B 

Name.             Derivation. 

>, 
c/2 

C.G.S 

Equivalent. 

E.  M.  F  

E 

Volt       Ampere  x  Ohm 

I08 

.926  standard  Daniell  cell. 

Resistance.  . 

R 

Ohm       Volt-:-  Ampere 

I09 

1.01367  B.  A.  Units  (?). 

Current  
Quantity.  .  .  . 
Capacity.  .  .  . 

C 

Q 

K 

Ampere  !     Volt  -4-  Ohm 
Coulomb  Ampere  per  sec. 
Farad.    Coulomb-*-  Volt 

TO-' 
io-  ' 

io-9 

(  .0000105  gram  of  hydro- 
(  gen  liberated  per  second. 

Power.  . 

P 

Watt       Volt  x  Ampere 

1C7 

.0013405  or  -  |?r  h.  -power. 

Work  I 

\V 

\    Volt  x  Coulomb 

I07 

•7373  foot-pounds. 

Heat  j 

Joule   "i     .              o     ,^1 
J             (    Ampere*  x  Ohm 

I07 

.238  calorie. 

13  FARADAY  (MICHAEL),  a  distinguished  chemist  and  natural  philosopher ;  born  in 
Newing'On,  England,  1791.     He  received  but  little  education,  and  while  young  was 
apprenticed  to  a  bookbinder.     While  working  at  this  trade,  a  scientific  book  fell  into 
his  hands,  which  he  read  with  avidity,  and  was  thus  led  to  devote  himself  to  the  study 
of  electricity.     In  1813  he  obtained  the  appointment  of  chemical  assistant  under  Sir 
Humphry  Davy  at  the  Royal  Institution.     In  1821  he  discovered  magnetic  rotation.    In 
1831  he  began  the  publication  of  his  Experimental  Researches  in  Electricity,  beginning 
with  the  induction  of  electric  currents  (151)  and  the  evolution  of  electricity  from  mag- 
netism  (73).      Three  years  later  he  discivered  the  principle  of  definite   electrolytic 
action  (154).     His  original  papers,  including  a  wide  range  of  contributions  to  modern 
science,  are  too  numerous  to  mention  in  detail.     In  1833  he  was  appointed  professor  of 
chemistry  in  the  Royal  Institution,  which  chair  he  continued  to  hold  until  his  death. 
He  was  a  member  of  many  learned  societies  of  Europe  and  America.     Died  1867. 

14  WATT  (JAMES),  an  eminent  mechanical  engineer,  born  at  Greenock,  Scotland, 
1736.     Under  his  father  he  acquired  a  knowledge  of  mathematical  instrument-making. 
When  nineteen  years  of  age  he  went  to  London,  but  soon  returned  and  settled  at 
Glasgow,  where,  under  the  patronage  of  the  university,  he  subsequently  immortalized 
himself  by  the  invention  of  the  steam-engine.     Died  1819. 

14  MUNROE  and  JAMIESON'S  Pocket-Book  of  Electrical  Rules  and  Tables,  p.  13*. 


74     Laws  and  Conditions  of  Electrical  Action. 

151.  Current    Induction. — An   electric   current   traversing   a 
conductor  has  a  capacity  of  setting  up  or  giving  rise  to  a  temporary 
current    in   a   neighboring    conductor.     This   effect  is   called    volta 
induction,  or,  more  commonly,  current  induction;    and  the  temporary 
current  thus   produced   is  called   the  induced  or  secondary  current. 
The   originating  current  in  such  a  case  is  termed  the  primary  or 
inducing  current.     This  effect  is  sometimes  observed  to  take  place 
between  two  long  and  well-insulated  telegraph  lines  which  are  situ- 
ated parallel  and   near  together  for  a  great  distance.     The  flow  of 
the  secondary  or  induced   current  is  in  a  direction  contrary  to  that 
of  the  primary  or  inducing  current. 

152.  Electrical    Dimensions   of  the  Voltaic  Cell.— The 
practical  value  of  any  type  of  cell  for  a  given  purpose  depends  upon 
what  is  known  as  its  electrical  dimensions,  and  upon  its  constancy.    The 
first  property  determines  the  quantity  of  electricity  which  it  is  capa- 
ble of  producing  in  a  given  time;  the  second  property  the  length  of 
time  it  is  capable  of  maintaining  such  action. 

153.— E.  M.  F.  and  Resistance  of  the  Cell.— The  elec- 
trical dimensions  of  a  cell  are  stated  in  terms  of  its  e.  m.  f.  and  its 
internal  resistance.  The  first  depends  upon  its  chemical  reaction, 
without  reference  to  size,  and  the  second  is  practically  uninfluenced 
by  any  considerations  other  than  the  conducting  power  of  the  solu- 
tions (126),  the  area  of  their  cross-section  (131)  and  the  tempera- 
ture.16 

The  duration  of  the  cell  depends  upon  the  quantity  of  material  it 
contains  and  upon  the  energy  of  the  chemical  action  within  it.  The 
gravity  cell,  described  in  Chapter  II.,  has  an  e.  m.  f.  of  1.07  to  1.08 
volts,  and  when  in  good  condition  an  average  resistance  of  3  to  4 
ohms. 

154.  Quantity  and  Cost  of  Materials  Consumed  in  the 
Battery. — The  subjoined  table  shows  the  theoretical  consumption 
and  deposition  of  material  in  each  gravity  cell  per  ampere  per 
hour,  in  fractions  of  an  avoirdupois  pound,  by  the  aid  of  which  the 
cost  of  producing  any  given  current  may  be  ascertained  when  the 
price  of  materials  is  known.17 

"  Heat  increases  the  e.  m.f.  of  a  sulphate  of  copper  cell ;  it  does  so  by  affecting  the 
solubilities  of  the  two  salts  and  supplying  externally  the  energy  absorbed  in  solution. 
Between  32°  and  52°  Fahr.  there  is  a  difference  of  .01  volt ;  between  50°  and  60°  also  .01, 
and  between  50°  and  100°  about  .025.  J.  T.  SPRAGUE  :  Electricity,  etc.  (2d  Ed.),  p.  141. 

17  The  electro-chemical  equivalent  of  zinc  is  here  taken  as  0.00033696  grams  per  am- 
pere per  second,  according  to  the  determinations  of  Rayleigh  and  Kohlrausch.  A 
table  of  electro-chemical  equivalents,  calculated  from  Rayleigh's  results,  is  given  by 
GEORGE  B.  PRESCOTT,  Jr.,  Electrical  Engineer,  iv.  7. 


Quantity  and  Cost  of  Materials  Consumed.     75 


TABLE    VII. 
CHEMICAL    EQUIVALENTS. 


Material. 

Atomic  weight. 

Lbs.  per  ampere  hour. 

Zinc  consumed  

64.0 

.0026749 

Sulphate  of  copper  consumed. 
Copper  deposited     .               .  . 

249-5 
6^.0 

.O1O28IO 

.OO25Q4Q 

Experience  shows  that,  owing  in  part  to  local  action  (57:  7),  the 
actual  consumption  of  zinc  is  greater  than  the  theoretical,  while  the 
consumption  of  s.  c.  and  the  deposit  of  copper  are  found  to  approxi- 
mate quite  closely  to  theoretical  requirements.  The  greater  part  of 
the  actual  zinc-waste  in  practice  is  due  to  the  unconsumed  residue 
of  each  zinc,  which  finally  has  to  be  thrown  out.  (6ia.) 

155.  The  following  examples  show  how  this  computation  is  made. 
Suppose  i  gravity  cell  is  employed  to  operate  a  certain  telegraphic 
instrument,  whose  magnetizing  coil  has  a  resistance  of  3.7  ohms, 
and  is  connected  with  the  cell  by  30  feet  of  No.  18  copper  wire. 
Required  the  theoretical  cost  per  month  of  maintaining  the  cell, 
when  used  from  8  a.m.  to  8  p.m.  every  day. 

Average  resistance  of  cell  (assumed  or  measured) 3  ohms. 

Resistance  of  30  ft.  No.  18  copper  wire  (table,  p.  94) 0.2 

Resistance  of  coil  of  instrument 3.7 


Total  resistance  of  circuit 6.9  ohms. 

Hence  1.07  volts  (i53)-s-6.9  ohms=o.i55  amperes. 


From  the  table  (154)  we  have : 

Sulph.  cop.  consumed..   .01028") 

Zinc  consumed 00267  ^  x  . I55  (amp. ) 

f     X  360  (hrs.) 
Cop.  deposited  (deduct)  . 00260  J 


.5736  Ibs.  at  10  cts.  —  $0.057 
.1490  Ibs.  at  16  cts.  —       .024 


$0.081 
.1451  Ibs.  at  16  cts.  ~      .023 

$0.058 

156.  Again,  suppose  two  telegraph  lines  supplied  from  one  battery 
of  100  cells,  each  line  carrying  a  current  of  25  milliamperes  (123); 
required  the  theoretical  consumption  per  month  of  material,  working 
24  hours  per  day. 

I  37.00  Ib.  at  10  cts.  rr  $3.70 
X  .05  (amp.)  j  Q  fa  \^  at  ,5  cts  _.  T>^ 
X  720  (hours)  <( 

X  ioo  cells.  $5 '24 

I  9.36  Ib.  at  16  cts.  —     1.50 


Sulph.  cop.  consumed. .   .01028"^ 
Zinc  consumed 00267 


Cop.  deposited  (deduct)  .00260. 


76      Laws  and  Conditions  of  Electrical  Action. 

We  find,  therefore,  that  the  theoretical  net  cost  of  materials  con- 
sumed in  a  battery  under  the  conditions  given,  is  less  than  4  cts.  per 
cell  per  month.  In  practice,  it  is  usually  from  4  to  5  cts.18 

157.  Production  of  Electricity  in  Proportion  to  Material 
Consumed. — An  idea  very  common  among  amateur  electricians  is 
that  it  may  be  possible  to  make  some  change  in  the  proportions  or 
arrangement  of  the  gravity  battery  by  which  its  power  may  be  in- 
creased without  a  corresponding  expenditure  of  material.     This  is  a 
fallacy.     Electricity  may  in  one  sense  be  regarded  as  a  constituent 
of  zinc,  which  is  set  free  when  that  metal  combines  with  oxygen,19  and 
hence  the  quantity  of  electricity  evolved  in  a  voltaic  cell  can  never 
exceed  a  certain  ratio  to  the  weight  of  zinc  consumed.     The  invaria- 
ble laws  of  chemical  combination  teach  us,  moreover,  that  the  con- 
sumption of  s.  c.   and   the  deposition   of  copper  must  in  all  cases 
maintain  a  fixed  ratio  to  the  consumption  of  zinc.* 

158.  Consumption   of  Material  in  a  Series  of  Cells.— 
Admitting  the    consumption  of  material  in  each  cell,  when  two  or 
more  cells  are  in  series,  to  be  in  proportion  to  the  quantity  of  current 
by  which  the  series  is  traversed,  it  follows  that  the  cost  of  material 
(the  external  resistance  remaining  constant)  must  be  as  the  square  of 
the  number  of  cells  in  series,  and  not  in  the  simple  ratio  of  the  num- 
ber of  cells.     Thus  if  we  increase  the  number  of  cells  threefold,  we 
have  three  times  as  many  cells  and  three  times  the  quantity  of  cur- 
rent traversing  each   cell,  so  that  the  consumption  of  material  will 
necessarily  be  ninefold. 

159.  Electrical  Dimensions  of  the  Edison-Lalande  Cell. 
—This  element  has  a  comparatively  low  e.  m.  ".  (0.70  to  0.75  volts), 

"but  on  the  other  hand  its  internal  resistance  is  very  small,  and  its 
local  action  almost  inappreciable.  Such  a  cell  is  well  suited  for  tel- 
egraphic work.  The  diagram  Fig.  59,  exhibits  the  results  01  a  test  of 
4  large  cells,  maintained  in  action  in  series  with  an  external  resist- 
ance of  0.8  ohms  continuously  for  108  hours.  Such  a  current  would 
suffice  to  supply  10  or  12  telegraph  lines  at  the  same  time. 

1 60.  Effect   of  Temperature   upon  the  Resistance  of 
Metallic  Conductors.— It  has  been  stated  (118)  that  the  resist- 
ance of  all  conductors  is  affected  by  temperature.     Unless  otherwise 
specified,  the  resistance  of  electrical   conductors    is  customarily  as- 
sumed to  be  taken  at  60°  Fahr. 

18  L.  BRADLEY  in  The   Telegrapher,  iii,  53  ;   F.  L.  POPE,  in  the  same,  vii,   345  ; 
Scientific  American  (n.  s.)  ix,  184. 

19  This  suggest-on  is  due  to  Latimer  Clark.     See  his  Electrical  Measurement,  p.  168. 
30  See  note  2,  p.  12  ;  also  (154). 


7 8      Laws  and  Conditions  of  Electrical  Action. 

161.  According    to    Miiller,    the    percentage    of  increase    in    re- 
sistance of  some  of  the  metals  most  employed  in  telegraphy  between 
o°  and  70°  Fahr.  is  as  follows  : 

Iron 8  per  cent. 

Copper 6.1  per  cent. 

Platinum 6  per  cent. 

The  difference  in  the  measured  resistance  of  a  telegraph  line  of 
iron  wire  may  therefore  vary  as  much  as  13  per  cent,  between  the 
extremes  of  summer  and  winter  temperature  in  the  northern  portions 
of  the  United  States.  The  resistance  of  German-silver  and  plati- 
num-silver alloys  vary  but  little  with  temperature,  and  hence  stand- 
ard resistances  are  made  from  wires  of  these  artificial  metals. 

162.  Effect  of  Temperature  upon  Resistance  of  Liquids. 
— The  liquid  mass  which  acts  as  a  conductor  in  a  voltaic  cell  under- 
goes considerable  variation  in  resistance  with  changes  of  tempera- 
ture.    Of  the    different    voltaic   combinations    in    general    use,  the 
sulphate  of  copper  cell  is  most  affected  in  this  way.     Hence  in  experi- 
ments with   this  cell,  it  is  important   that  the  temperature  be  kept 
constant,  or  that  frequent  measurements  should  be  made  of  the  in- 
ternal resistance  and  allowance  made  therefor. 

163.  Effect  of  Temperature  upon  Resistance  of  Daniell 
Cell. — Three  series  of  tests  of  the  Daniell  sulphate  of  copper  cell 
were  made   by  Preece ;   in  the  two  first  cases,  the  s.  c.  solution  was 
saturated  at  all  temperatures,  while  the  s.  z.  solution  had  the  same 
density   throughout  the   period   of  observation,  being   saturated  at 
about   57°  Fahr.     In   the  third  case  both  solutions  remained  satu- 
rated at  about   50°  Fahr.     The   results   are  given   in  the  diagram, 
Fig.  590.     The  curve  ABCDE  corresponds  to  the  case  in  which  the 
s.  c.  solution  was  saturated  at  all  temperatures,  while  the  s.  z.  solution 
was  of  constant  density.     The  curve  abed  corresponds  to  the  case  in 
which  both  solutions  remained  unaltered  in  density.     The  direction 
of  the  arrows  indicates  the  order  of  the  experiments.     In  the  curve 
ABCDE,  the  portion  AB  represents  the  result  obtained  by  heating 
the  cell  from  about  52°  to  211°  Fahr.  (near  the  boiling  point  of 
water),  and  the  portion  BC  that  obtained  while  the  same  cell  -,vas 
being  cooled   from   211°  to  35°  Fahr.,  nearly  the  freezing  point  of 
water.     A  similar  explanation  applies  to  the  curve  abcde. 

164.  These  curves  clearly  show  : 

(a)  That  when  the  temperature  of  a  Daniell  cell  is  raised  from 
the  freezing  to  the  boiling  point  of  water,  the  internal  resistance  of 
the  cell  decreases,  abruptly  at  first,  but  more  gradually  afterward, 
falling  from  2.12  to  .66  ohms,  or  more  than  one-third. 


Effect  of  Temperature  upon  Battery  Resistance.     79 


(If)  That  when  a  cell  which  has  been  thus  heated  is  cooled,  the 
resistance  increases  at  a  more  rapid  rate  than  it  fell  off  while  being 
heated;  in  other  words,  the  resistance  of  a  Daniell  cell,  within  the 
range  of  temperature  experimented  upon,  is  smaller  before  it  has 
been  heated  to  a  high  temperature  than  afterward,  provided  the 
heating  and  cooling  be  not  done  too  slowly. 


X 


60° 


TEMP.   FAHRENHEIT 

104°          122°          140°         158° 


176 


194  212° 


*l 


c! 
Vi 


\ 


\ 


10 


r.'O 


80° 


90" 


30  40°  60  60°  70 

TEMP.  CENTIGRADE 
FIG.  59  a.    Effect  of  Temperature  upon  Resistance  of  Voltaic  Cell. — PREECE. 


100' 


(c)  That  if  the  cell  thus  cooled  down  be  left  undisturbed  at  a 
given  temperature,  the  resistance  of  the  cell  slowly  diminishes  until 
at  last,  at  the  end  of  a  certain  period  (40  to  50  hours),  it  returns  to 
the  value  which  it  had  before  having  been  heated. 

(//)  That  the  resistance  of  a  Daniell  cell  is  considerably  less 
when  the  s.  c.  solution  is  more  dense  than  when  it  is  less  dense,  at 
any  temperature.21 

21  W.  H.   PREECE  :  Effect  of  Temperature  on  the  e.  m.f.  and  Resistance  of  Bait* 
ries.     Proc.  Royal  Soc.  1883 ;  Lond.  Electrician,  x.  367. 


CHAPTER  VI. 

THE    LAWS    OF    ELECTRO-MAGNETISM. 

165.  The  Electro-Magnet,  as  improved  by  Henry,1  forms  the  most 
essential  part  of  every  telegraphic  receiving  instrument,  and  is  the 
instrumentality  by  means  of  which  the  energy  of  the  electric  current 
is  transformed  into  mechanical  power,  and  is  made  to  produce  phys- 
ical effects  appreciable  by  the  senses. 

Nearly  every  fact  of  importance  in  connection  with  the  phenomena 
of  electro-magnetism  has  been  known  to  experimenters  and  observ- 
ers for  half  a  century,  but  the  apparently  anomalous  and  contradic- 

i  HENRY  (JOSEPH),  LL.D.,  born  Albany,  N.  Y.,  1799;  educated  in  the  common 
schools  of  that  city  and  in  the  Albany  Academy,  in  which  he  became  professor  of 
mathematics  (1826),  and  almost  immediately  entered  upon  a  course  of  experimental 
investigation,  during  which  he  made  numerous  and  important  discoveries  in  elec- 
tricity and  magnetism.  Although  at  this  date  the  electro-magnet  had  become  in  a 
certain  sense  known,  from  the  researches  of  Sturgeon  ( Transactions  Soc.  Arts,  xliii. ; 
Nov.  1825),  it  was  but  a  philosophic  toy,  in  which  a  feeble  magnetic  excitation  was 
produced  by  currents  of  small  e.  m.  f.  in  a  short  circuit.  Henry's  first  success  was 
the  invention  of  the  electro-magnet  as  we  now  know  it,  a  horse-shoe  of  soft  iron  sur- 
rounded by  many  turns  of  insulated  copper  wire  arranged  in  concentric  layers  (186), 
a  construction  which  no  subsequent  invention  has  essentially  modified.  He  next 
demonstrated  that  the  difficulty  of  exciting  magnetic  energy  at  a  distance  by  an 
electric  current,  which  had  led  Barlow  in  1824  to  pronounce  the  idea  of  an  electric 
telegraph  "  chimerical,"  may  be  completely  overcome  by  the  use  of  a  battery  of  a 
sufficient  number  of  cells,  arranged  in  series  (107),  provided  the  electro-magnet  be  pro- 
vided with  a  helix  having  a  sufficient  number  of  turns.  It  was  the  invention  of 
Henry's  electro-magnet  which  first  made  the  electric  telegraph  a  commercial  possi- 
bility, and  it  is  worthy  of  note  that  in  an  article  published  in  1831  (Amer.  your. 
Science,  xix.  400),  he  pointed  out  the  applicability  of  the  long-coil  magnet  to  this 
purpose.  During1  the  same  year  he  constructed  an  apparatus  for  giving  signals  at 
a  distance,  which  was  operated  through  more  than  a  mile  of  wire  carried  around  the 
walls  of  a  room  in  the  Albany  Academy.  This  apparatus  embodied  all  the  essential 
principles  of  the  practical  telegraph  of  to-day.  The  signals  were  produced  by  the 
polarized  armature  of  an  electro-magnet  which  was  made  to  vibrate  by  reversal  of  the 
current  (201)  and  to  strike  a  bell.  In  1832  he  discovered  the  induction  of  a  current 
in  a  coiled  conductor  upon  itself  (196).  In  1832  he  was  elected  professor  of  natural 
philosophy  in  the  College  of  New  Jersey,  at  Princeton,  and  in  1846  first  secretary  of 
the  Smithsonian  Institution  in  Washington,  which  honorable  position  he  continued  to 
hotd  until  his  death  in  1878.  His  collected  scientific  papers  have  been  published  in 
2  vols.,  Washington  (1886).  For  many  particulars  of  interest  respecting  the  contribu- 
tions of  Henry  to  the  invention  of  the  electric  telegraph,  see  Life  and  Work  of  Jo- 
seph Henry^  by  F.  L.  POPE,  and  "The  American  Inventors  of  the  Telegraph,"  by 
the  same,  in  the  Century  Magazine,  xxxv.  924  (April,  1888).  It  has  recently  become 
known  that  he  was  the  first  to  discover  the  phenomenon  of  magneto  electricity  (62). 
See  papers  by  MARY  A.  HKMKY,  N.  Y.  Elect.  Engineer,  xiii.  27  etseq. 

80 


Elements  of  the  Electro-Magnet. 


81 


tory  character  of  mrmy  of  the  results  obtained  has  been  very  puzzling 
to  the  student.  It  was  not  until  after  the  conception  of  the  exist- 
ence of  a  magnetic  circuit  (178),  analogous  in  many  of  its  proper- 
ties to  that  of  the  electric  circuit,  originally  due  to  Joule,2  had  been 
definitely  formulated  in  1873  by  Rowland,3  and  its  truth  confirmed 
by  the  subsequent  researches  of  Bonsanquet 4  and  others,  that  it 
became  possible  to  suggest  an  adequate  explanation  for  many  of  the 
singular  and  apparently  unaccountable  facts  which  had  been  noticed 
by  investigators. 

166.  Elements  of  the  Electro-Magnet. — The  electro-mag- 
net may  conveniently  be  regarded  as  comprising  three  distinct  ele- 
ments,  the    laws    of   each    of   which   must   be   separately  studied, 
although  they  all  enter  into  the  general  result.     These  elements  are 
(i)  the  wire,  (2)  the  iron,  and  (3)  the  current. 

167.  It  has  been  stated  (85,  d}  that  when  a  piece  of  soft  iron  is 
spirally  encircled  by  a  conductor,  it  is  rendered    magnetic   by  the 
passage  of  a  current  through  this  conductor.     Such  an  organization 
constitutes  an  electro -magnet  in  its  elementary  form. 

168.  Polarity  of  Electro-Magnet  Determined  by  Direc- 
tion   of  Current. — The  position  of  the  respective  poles  of  an 
electro-magnet    is    in 

all  cases  determined 
by  the  direction  of  the 
magnetizing  current. 
It  is  usual  to  coil  the 
conducting  wire, 
coated  or  insulated ,  with  nonconducting  material,  into  what  is 
termed  a  right-handed  helix,  shown  diagrammatically  in  Fig.  60,  in 
which  the  conventional  direction  of  the  current  (31)  is  indicated  bv 
the  arrows,  while  the  respective  north  and  south  poles  induced 
thereby  are  designated  by  the  letters  N  and  S  Thus,  if  the  current 

flows  around  the  iron 
in  the  direction  of  the 
hands  of  a  watch,  the 
north  pole  will  be  at 
the  distant  end  of  the 

FIG.  61.     Electro-Magnet  with  Left-handed  Helix. 

iron.      If  the  current 
be  made  to  flow  in  the  opposite  direction,  as  in  Fig.  61,  the  polarity 

2  Sturgeon's  Annals,  iv.  58. 

a  H.  A.  ROWLAND  :  On  the  Magnetic  Permeability  of  Iron,  Phil.  Mag.  (4th  series), 
xlvi.  140 ;  also  in  the  same,  i,  257,  348. 

4  R.  H.  M.  BONSANQUET  :  On  Magneto- Motive  Force,  Phil.  Mag.  (sth  series),  xv. 
205 ;  the  same,  On  Electro-Magnets,  Electrician  (  ond.),  xiv.  291,  351. 


FIG.  60.     Electro-Magnet  with  Right-handed  Helix. 


82  The  Laws  of  Electro- Magnetism. 

of  the  iron  is  reversed,  the  north  pole  now  being  at  the  end  where 
the  south  pole  was  before,  and  vice  versa. 

169.  Lines  of  Force  as  a   Measure  of   the  Magnetic 
Field. — It  has  been  explained  (93)  that  a  conductor  conveying  an 
electric  current  is  surrounded  by  a  field  of  magnetic  force,  and  that 
in  such  a  field,  the  lines  of  force  are  concentric  with  the  conductor. 
These  lines  of  force  may  be  regarded  as  units,  in  terms  of  which 
magnetism  may  be  expressed  and  measured. 

The  direction  and  polarity  of  the  magnetic  force  is  indicated  by 
the  direction  and  polarity  of  the  lines,  the  total  number  of  its  lines 
is  a  measure  of  the  total  quantity  of  magnetism,  while  the  number 
of  them  contained  in  a  given  unit  of  area,  measured  in  a  direction 
perpendicular  to  their  direction,  is  a  measure  of  the  intensity  of 
magnetism  at  that  point. 

This  conception  of  magnetic  force  may,  perhaps,  be  better  understood  if 
compared  to  the  force  of  gravity  similarly  represented.  Imagine  a  heavy 
body  suspended  in  the  air,  and  suppose  every  cubic  inch  of  the  material  of 
which  the  body  is  composed  to  weigh  one  pound.  If  an  imaginary  line  be 
drawn  to  the  earth  from  the  center  of  gravity  of  each  cubic  inch  of  the  sus- 
pended body,  the  direction  of  these  lines  would  represent  the  direction  of 
the  force  of  gravity  ;  their  total  number  would  represent  the  total  force  in 
pounds  ;  while  their  density,  or  the  number  of  lines  per  square  inch  area 
(measured  perpendicularly  to  their  direction),  would  represent  the  intensity 
of  the  force  at  that  point.  In  precisely  the  same  way  as  these  lines  repre- 
sent the  direction,  amount,  and  intensity  of  the  force  of  gravity  in  that  body, 
so  do  the  lines  of  magnetic  force  represent  the  direction,  amount,  and  inten- 
sity of  magnetism,  except  that  in  the  latter  there  is  no  constant  direction  of 
action  such  as  the  downward  force  of  gravity,  the  lines  of  force  acting  in 
both  directions,  as  if  trying  to  shorten  their  circuit,  like  a  stretched  rubber 
ring.  The  lines  do  not  exist  as  such,  any  more  than  they  do  in  the  analogy 
of  the  force  of  gravity  ;  it  is  merely  a  convenient  way  of  representing  mag- 
netism in  order  to  facilitate  the  conception  and  computation  of  problems. — 
CARL  HERING  :  Principles  of  Dynamo-Electric  Machines,  18. 

170.  An  accurate  knowledge  of  the  characteristics  of  magnetism 
is  of  great  importance  in  the  designing  and  construction  of  dynamo- 
electric  machinery,  and  it  fortunately  happens  that  recent  researches 
in   connection  with   this  class   of  work   have   greatly  enlarged   our 
practical   knowledge   of  the   laws  and   conditions   of  magnetic  and 
electro-magnetic  action  as  applied  to  telegraphic  and  other  apparatus 
of  like  character. 

Provided  we  are  able  to  calculate  the  intensity  of  the  magnetic 
field  which  is  produced  by  the  influence  of  a  known  current,  we 
have  the  means  of  calculating  also  the  intensity  of  magnetism  in  an 
iron  core  placed  within  that  field.  When,  however,  the  magnetiza- 


Unit  of  Magnetism.  83 

tion  approaches  the  limit  of  intensity  which  the  soft  iron  is  capable 
of  receiving,  the  actual  magnetization  always  falls  short  of  the  theo- 
retical magnetization  as  calculated  by  this  rule. 

171.  Unit  of  Magnetism. — It  is  customary  to  express  intensity 
of  magnetism,  or  magnetic  density,  as  it  is  sometimes  termed,  by  the 
number  of  lines  of  force  per  unit  of  cross  sectional  area,  measured  per- 
pendicularly to  their  direction.      The  unit  of  magnetism  is  the  equiv- 
alent of  a  single  one  of  these  lines  of  force,  and  is  that  quantity  of 
magnetism  which  passes  through  one  square  centimetre  of  the  cross- 
section  of  a  magnetic  field  whose  intensity  is  unity.     It  has  been 
proposed  to  call  the  magnetic  unit  the  gauss:'     To  illustrate,  suppose 
a  circular  loop  of  wire  like  that  shown  in  Fig.  33,  p.  41,  having  a 
-diameter  of  10  centimetres  (3.9  in.),  to  be  traversed  by  a  current  of 
7.958  amperes.     The  quantity  of  magnetism  passing  through  an  area 
of  i   sq.  cm.  at  the  center  of  the  loop  will  be  i  unit.6     A  magnetic 
field  in  which  the  number  of  parallel  lines  of  force  per  unit  area  is 
the   same   in   every  part  is  termed  a  field  of  uniform  intensity,  or 
briefly,  a  uniform  field,     A  good  illustration  of  such  a  field  is  that  of 
the  earth  referred  to  in  (94).      The  field  inclosed  within  a  circular 
loop  of  wire  like  Fig.  33  is  not  uniform,  but  varies  in  different  parts, 
being  most  intense  near  the  circumference  and  least  in  the  center. 

172.  Magneto-Motive  Force. — Recurring  again  to  the  electric 
conductor  surrounded  by  concentric  lines  of  force,  as  shown  in  Fig. 
32,  p.  39,  it  is  n6t  difficult  to  understand  that  if  we  coil  such  aconduc- 

5  GAUSS  (KARL  FRIEDRICH),  born  in  Brunswick,  Germany,  April  30,  1777.  When 
very  young  was  distinguished  for  his  mathematical  attainments  ;  became  Professor  of 
Astronomy  and  Director  of  the  Observatory  in  Gottingen,  1807 ;  was  made,  in  1816, 
Court  Councilor  and  in  1845  a  Privy  Councilor  of  Hanover;  after  1821  made  impor- 
tant improvements  in  geodetic  methods  and  instruments  ;  and  after  1831  devoted  much 
attention  to  the  study  of  terrestrial  magnetism.  In  1833,  with  the  assistance  of  his 
coadjutor,  WILHELM  EDUARD  WEBER,  Professor  of  Physics  in  the  University  of  Got- 
tingen, he  constructed  an  electric  telegraph  more  than  a  mile  in  length,  extending 
from  the  Physical  Cabinet  to  the  Observatory  in  that  city.  This  telegraph  was  re- 
markable as  being  the  first  in  which  magneto-electricity  (73)  was  used  ;  for  the  inge- 
nious but  simple  method  employed  of  using  a  ray  of  light  as  an  index  of  the  movement 
of  the  galvanometer  needle  (a  plan  long  afterward  adopted  by  Sir  William  Thomson 
in  his  well-known  mirror  galvanometer)  ;  and  last,  though  not  least,  as  having  had  an 
actual  existence  for  several  years  ;  for  although  at  first  intended  for  scientific  purposes 
only,  it  soon  came  to  be  employed  as  a  means  of  ordinary  correspondence  as  well. 
(SABINE  :  The  Electric  Telegraph,  p.  27.)  Gauss  died  at  Gottingen,  1855. 

«  What  is  known  among  manufacturers  of  electrical  machinery  as  the  English  unit 
of  magnetic  induction  was  proposed  by  GISBERT  KAPP  (Jour.  Tel.  Eng.,  xv.  518). 
The  unit  line  of  force  adopted  is  equal  to  6,000  c.  g.  s.  lines,  the  sectional  area  of  the 
iron  being  taken  in  square  inches.  The  English  unit,  therefore,  is  one  of  these  as- 
sumed lines  per  square  inch,  and  is  commonly  termed  a  Kapp  line. 

i  Kapp  line  per  sq.  in.  —  930  c.  g.  s.  lines  per  sq.  cm. 

i  English  unit  =  930  c.  g.  s.  units  of  magnetic  induction. 


84  The  Laws  of  Electro-Magnetism. 

tor  into  an  elongated  helix  or  spiral,  technically  termed  a  solenoid^ 
Fig.  62,  and  cause  the  current  to  traverse  it  in  the  direction  indicated 
by  the  arrows,  the  lines  offeree  inclosed  within  the  helix,  being  the 
resultant  of  those  of  the  separate  turns,  assume  the  form  represented 


FIG.  62.     Direction  of  Lines  of  Force  within  a  Solenoid. 


in  the  figure.  In  the  drawing,  for  convenience  of  illustration,  only  a 
part  of  each  line  of  force  is  shown,  but  it  must  be  borne  in  mind  that 
every  line  is  in  fact  endless,  forming  a  complete  magnetic  closed  cir- 
cuit returning  into  itself,  so  that  different  lines  can  never  under  any 
circumstances  intersect  each  other.  The  value  of  the  current  in  am- 
peres being  known,  a  corresponding  field  of  definite  intensity  is  set 
up  within  the  helix.  The  intensity,  or,  as  Bonsanquet  calls  it,  the 
magneto-motive  force  of  the  field,  may  be  readily  calculated  by  the  fol- 
lowing : 

RULE. — Multiply  the  number  of  turns  in  the  helix  by  the  current  in  am- 
peres and  divide  this  product  (ampere-turns)  by  the  length  of  the  helix  in 
centimetres  ;  multiply  the  quotient  by  1.2566,  and  the  product  will  be  the 
intensity  expressed  in  lines  of  force  per  square  centimetre,  or  if  the  length  be 
taken  in  inches,  the  multiplier  0.3132  will  give  the  quotient  in  lines  per  square 
inch. 


FIG.  63.  Lines  of  Force  traversing  Iron  Bar  within  the  Solenoid. 

173.  Effect  of  Iron  in  the  Helix. — If  now  a  soft  iron  core  be 
placed  within  the  same  helix,  as  shown  in  Fig.  63,  the  intensity  of 
the  field  is  materially  increased,  or  in  other  words  the  number  of  lines- 


Effect  of  Magnetization  upon  Soft  Iron.        85 


of  force  per  unit  of  cross-sectional  area  is  greatly  augmented.  The 
strength  of  field  due  to  the  presence  of  the  coil  and  its  contained 
iron  is  termed  magnetic  induction.  The  difference  between  the  num- 
ber of  lines  per  unit  of  area,  with  and  without  the  iron,  evidently  gives 
the  value  of  the  magneto-motive  force  due  to  the  iron  alone.  This 
difference  may  be  stated  roughly  as  about  100  to  i  for  soft  iron  of 
average  good  quality. 

174.  Effect  of  Magnetization  upon  Soft  Iron. —The 
graphic  diagram,  Fig.  64,  was  plotted  from  a  series  of  observations 
made  with  a  magnetometer -7  upon  a  rod  of  unannealed  iron  10  cm 
(3.9  in.)  long  and 
4.3  mm.  (o.  169  in.) 
in  diameter,  placed 
within  a  helix  of 
135  turns.8  The 
values  of  the  cur- 
rent in  ampere 
turns  are  plotted 
out  upon  the  hori- 
zontal, and  those  g 
of  the  magnetic 
forces  upon  the 
vertical  scale.  The 
resulting  curve 
takes  the  form 
shown  in  the  figure 
by  the  line  o  B. 
It  will  be  seen  to 
consist  of  two 
parts;  one  part 
which  rises  at  a  more  or  less  steep  angle,  and  which  for  some -dis- 
tance from  its  origin  at  o  continues  nearly  straight  to  the  point  i, 
and  another  part  B  2,  also  nearly  straight,  but  which  is  inclined  at 
a  much  less  angle  to  the  horizontal,  these  two  parts  being  joined  by 

7  The  magnetometer  is  an  instrument  for  the  measurement  and  comparison  of 
magnetic  forces.  It  consists  essentially  of  a  magnet  or  needle  delicately  suspended 
in  the  magnetic  meridian,  and  provided  with  a  pointer  or  index,  usually  in  the  form  of 
a  ray  of  light  reflected  by  a  small  mirror.  By  placing  the  stationary  magnet  whose 
force  is  to  be  determined  at  a  measured  distance  east  or  west  of  the  suspended  needle, 
with  one  of  its  poles  pointing  directly  toward  it,  it  is  easy,  by  observing  the  angle  of 
deflection  of  the  needle,  to  measure  the  attractive  force  of  the  magnet  pole.  For  a 
simple  apparatus  and  method  of  performing  this  operation  see  J.  TROWBRIDGE  :  New 
Physics,  131. 

s  KENNELLY  and  WILKINSON  :  Practical  Notes  for  Electric  Students,  aao. 


FIG.  64.     Relation  of  Current  to  Magnetic  Force. 


86 


The  Laws  of  Electro-Magnetism. 


a  curved  portion  i,  2.  The  first-mentioned  part  of  the  curve  corre- 
sponds to  the  state  of  things  when  the  iron  core  is  unsaturated ;  the 
latter  part  to  the  state  when  the  core  is  more  than  half  saturated  ; 
while  the  curved  intermediate  portion  corresponds  to  the  intermedi- 
ate state  during  which  the  core  is  approaching  saturation  (177).  In 
the  curve  of  results  of  an  electro-magnet  two  effects  are  in  reality 
combined ;  that  of  the  magnetism  of  the  iron  core,  and  that  of  the 
magnetic  action  of  the  coils  through  which  the  current  is  flowing  ; 
this  joint  effect  is  shown  in  the  dotted  line.  It  is  easy  to  separate 
these  two  values,  for  if  the  iron  core  be  removed,  and  the  magnetic 
effect  of  the  coils  alone  be  observed,  a  new  set  of  data  are  obtained 
which,  when  plotted  out,  will  yield  the  more  gently  sloping  line 
o  C.  From  this  line  two  conclusions  may  be  drawn :  it  slopes  at  a 
small  angle,  because  (i)  the  magnetic  effect  of  the  coils  is  small 
compared  with  that  of  the  iron  core.  It  is  quite  straight,  because 
(2)  the  magnetic  effect  of  a  coil  (which  of  course  is  not  capable  of 
saturation)  is  exactly  proportional  to  the  strength  of  the  current  by 
which  it  is  traversed,  throughout  the  entire  range  of  the  experi- 
ment. 

175.  The  following  series  of  determinations,  made  with  a  coil  of 
500  turns  surrounding  an  iron  core  10  cm.  (4  in.)  long  and  i  cm. 
(13-32  in.)  in  diameter,  further  illustrate  this  matter.  The  figures 
in  the  last  column  are  the  values  of  the  magnetic  moment**  as  calcu- 
lated from  the  deflections  produced  in  a  magnetometer.10 


Amperes. 

Ampere-turns. 

Magnetic  Moment. 

O.OO 

0 

128 

O.22 

no 

1224 

0-39 

195 

1920 

0.98 

49° 

4608 

1-33 

665 

5924 

3-65 

1825 

17472 

4.6 

2300 

21088 

9.2 

4600 

27875 

9.4 

4700 

28750 

The  above  values,  when  plotted  out,  will  give  curves  similar  in 
form  to  those  shown  in  Fig.  64.     The  values  of  magnetic  moment 

9  The    magnetic  moment  of  a  magnet  in  c.  g.  s.  measure  is  the  product  of  the 
strength  of  its  magnetic  pole  in  dynes  (191)  multiplied  by  the  distance  between  its 
poles  in  centimetres.     The  intensity  of  magnetization  of  a  magnet  is  the  ratio  of  its 
magnetic  moment  to  its  volume. 

10  SILVANUS  P.  THOMPSON  :   Dynamo- Electric  Machinery,  (2nd  edition),  355. 


The  Magnetic  Circuit.  87 

for  telegraphic  magnets,  when  plotted  out  in  the  same  way.  will  fall 
upon  the  lower  half  of  the  steep,  straight  portion  of  such  a  curve." 

176.  Magnetic   Saturation. — It  will  be  seen,  therefore,  that 
the  proportion  of  ampere-turns  to  magnetic  intensity,  referred  to  in 
(174),  holds  good  only  through  a  certain  range  of  magnetic  increase. 
When  the  intensity  has  reached  a  certain  point,  the  iron  becomes, 
from  that  point  onward,  less  and  less  susceptible  to  further  magneti- 
zation, and  though,  strictly  speaking,  the  point  of  absolute  satura- 
tion can  never  be  reached,  there  is  a  practical  limit  which  cannot  be 
exceeded.1-    The  approach  of  saturation  is  well  exhibited  in  the 
core  curve  in  Fig.  64,  which  begins  to  deflect  when  the  magnetizing 
force  reaches  the  vicinity  of  500  ampere-turns. 

The  cores  of  the  electro-magnets  of  modern  telegraphic  apparatus  seldom 
exceed  0.5  in.  in  diameter.  It  has  been  experimentally  proved  that  the 
approach  of  saturation  in  a  core  of  this  dimension  is  not  reached  with  less 
tuan  about  500  ampere-turns,  which  is  some  3  times  the  degree  of  magneti- 
zation ordinarily  employed  in  telegraph  magnets  used  in  local  circuits,  while 
that  employed  in  magnets  used  in  main  circuits  is  still  less. 

177.  Magnetization  Proportional  to  Ampere -turns.— 

An  important  principle  in  electro-magnetism  is,  that  precisely  the 
same  magnetic  effect  may  be  obtained  from  a  few  turns  of  wire  and 
a  large  volume  of  current  as  from  a  great  number  of  turns  and  a 
small  current,  provided  only  that  the  number  of  ampere-turns  remains 
the  same.  This  necessarily  follows  from  the  fact  that  the  same 
amount  of  work  is  done  in  the  wire 
by  the  circuit  in  each  case  (92).  -L/* 

178.  The  Magnetic  Circuit. 
— In    the    practical    application    of 
the  electro-magnet    for  telegraphic 
and  other  like  uses,  it  is  not  usual 
to  make  it  in  the  form  of  a  straight 
bar.     Much  better   results   are   at- 
tained by  bending  the  bar  into  the 
form  of  a   |J>  or  "horseshoe,"  as 
shown  in  Fig.  65,  which  enables  an 

armature  to  be  applied  to  it  in  such 

rr.  .          Fro,  65.    Principle  of  Horseshoe  Electro- 

a    manner  as  to   form   a  complete  Magnet. 

11  For  an  experimental  investigation  of  the  relation  between  the  diameter  of  the 
core,  the  total  magnetizing  force  of  the  coil,  and  the  force  of  attraction,  see  paper  by 
E.  L.  FRENCH  :  Electrician  and  Elect.  Eng.,  v.  445. 

12  The  limit  of  magnetization  in  good  wrought-iron  is  about  125,000  (c.  g.  s.) 
magnetic  lines  per  sq.  in.,  or  20,000  per  sq.  cm. — S.  P.  THOMPSON  :  The  Electromagnet, 
32,  83;  ibid.,  Dynamo-Electric  Machinery  (4th  Ed.),  148,  149. 


88  The  Laws  of  Electro-Magnetism* 

magnetic  circuit.  Inasmuch  as  magnetism  is  now  known  to  be  a  phe- 
nomenon pertaining  to  the  internal  molecular  structure  of  iron,  the 
preferable  method  of  treating  the  subject  is  to  look  upon  that  metal 
as  a  substance  which  is  a  good  conductor  of  the  magnetic  lines  of 
force,  or,  as  it  is  expressed  in  madern  scientific  language,  possessing 
a  high  degree  of  magnetic  permeability.^ 

179.  Magnetic    Permeability. — This   characteristic   may   be 
best  defined  as  a  numerical  co-efficient  which  expresses  the  ratio  be- 
tween the  number  of  magnetic  lines  formed  in  a  space  containing 
nothing  but  air,  as  in  Fig.  62,  and  as  denoted  by  the  value  of  the  line 
o  B  in  Fig.  64,  and  the  number  formed  in  a  space  filled  with  a  given 
quality  of  iron,  as  in  Fig.  63,  and  as  denoted  by  the  value  of  the 
dotted  line  in  Fig.  64-14     This  ratio  differs  for  different  qualities  of 
iron,  and   hence  we  say  that  the   permeability  of  the   iron   differs 
accordingly. 

The  higher  the  co-efficient  of  permeability,  the  less,  so  to  speak, 
is  the  magnetic  resistance,  and  the  more  suitable  is  the  iron  for  the 
purposes  of  an  electro-magnet.  On  the  other  hand,  the  permeability 
of  air  and  of  most  substances  other  than  iron  is  comparatively  very 
small. 

180.  Law  of  the  Magnetic  Circuit. — In  (172)  the  method 
of  calculating  the  magneto-motive  force  of  a  magnetic  circuit  has 
been  given.     We  have  next  to  find  the  resistance  which  the  magnetic 
circuit  offers  to  the  passage  of  the  lines  of  force,  a  property  which 
has  appropriately  been  termed  by  Dr.  O.  J.  Lodge  magnetic  reluc- 
tance.    The  total  magnetism  of  the  circuit,  called  the  magnetic  flux, 
will  be  the  quotient  of  the  magneto-motive  force  divided  by  the  reluc- 
tance.    The  similarity  of  the  law  of  the  magnetic  circuit  to  the  law 

of  the  electric  circuit,  heretofore  referred  to 
as  Ohm's  law  (127),  will  be  apparent  upon 
inspection. 

181.  Determination  of  Magnetic 
Reluctance. — If  the  magnetic  circuit  is 
a  simple  closed  ring  of  iron,  the  magnetic 
reluctance  may  be  calculated  precisely  in 
the  same  manner  that  we  calculate  the  re- 
sistance of  an  electric  circuit.  The  value  of 
the  reluctance  is  directly  in  proportion  to 

FIG.  66.   Lines  of  Force  in  End-  .  .    J  , 

less  iron  Ring.  the  length  of  the  iron,  inversely  as  the  area 

"  FARADAY  :  Exper.  Res.,  iii.  426 ;  Sir  W.  THOMSON  :  Papers  on  Electricity  and 
Magnetism,  484. 

14  ROWLAND  :  Phil.  Mag.  (5th  series),  xlvi.  140. 


Ratio,  of  Attractive  Force  to  Distance.         89 

of  its  cross-section,  and  is  also  inversely  proportional  to  its  perme- 
ability. But  if,  instead  of  a  homogeneous  ring  of  iron,  the  circuit 
be  made  up  of  different  parts,  differing  in  their  magnetic  reluc- 
tance, it  becomes  necessary  to  determine  the  reluctance  of  each 
part  separately,  and  then  add  them  together,  as  in  the  case  of  an 
electric  circuit  of  like  character  (118).  For  example,  Fig.  66 
shows  the  lines  of  force  in  an  endless  iron  ring.  Fig.  67  is  a 
similar  ring  cut  in  two,  leaving  an  air-gap 
between  the  severed  ends.  It  has  been 
stated  that  the  permeability  of  air  is  far 
less  than  that  of  iron  (179).  The  reluc- 
tance of  the  air-gaps  to  the  magnetic  lines 
may  be  taken  roughly  at  i  oo  times  that  of 
a  mass  of  soft  iron  of  good  quality  of  the 
same  form  and  dimensions.  The  case  of 
the  divided  ring  of  Fig.  67  is  equivalent  to 
that  of  the  horseshoe  magnet  and  its  arma- 

-~        -  ,  FIG.  67.    Lines  of  Force  Cross- 

ture  shown  in  Fig.  65,  when  the  armature  inK  Air-gaP  in  Magnetized  Ring, 
is  a  little  way  removed  from  the  poles,  and 

is  the  condition  which  is  constantly  met  within  the  operation  of 
ordinary  telegraphic  apparatus.  The  lines  of  force  traverse  the 
armature  in  passing  from  one  pole  to  the  other. 

182.  Ratio  of  Attractive  Force  to  Distance. — It  is  stated 
in  many  text-books  that  the  attractive  force  exerted  by  an  electro- 
magnet upon  its  armature  varies  inversely  as  the  square  of  the  dis- 
tance between  them.  This  proposition,  known  as  Coulomb's  law, 
would  be  true,  if  it  were  true  that  the  magnetic  forces  are  concen- 
trated at  a  focal  point  in  each  pole,  and  that  this  disposition  of  it 
remains  unchanged  by  the  movement  of  the  parts  in  response  to 
the  magnetic  attraction.  But  in  fact  there  is  not,  and  from  the 
nature  of  the  case  cannot  be,  any  one  law  which  correctly  expresses 
this  relation  under  all  conditions.  It  necessarily  differs  with  every 
alteration  in  the  form  of  magnet  and  armature,  and  with  every 
change  in  their  positions  with  reference  to  each  other.  This  is  well 
shown  in  experiments1"'  made  with  an  electro-magnet  having  a  core 
formed  from  a  round  bar  19  in.  long  and  i  in.  thick,  bent  into  a 
horseshoe,  with  its  poles  1.25  in.  apart.  The  distance  of  the  arma- 
ture from  the  poles  was  determined  by  the  interposition  of  sheets  of 
rolled  brass  .00416  in.  thick,  the  required  number  of  these  sheets 
for  each  experiment  being  strongly  pressed  together  and  soldered 
at  the  edges.  The  following  table  gives  the  results  in  weights  lifted, 

15  DANIEL  DAVIS,  Jr.:  Manual  of  Magnetism  (i2th  Ed.,   1857),  152. 


9o 


The  Laws  of  Electro-Magnetism. 


with  various  thicknesses  of  brass  sheets,  numbered  from  i  to  10, 
interposed  between  the  magnet  and  the  armature  : 


Distance. 

Weight  Lifted,  Grains. 

Product 

o 

82,000 

I 

35,000 

35,000 

2 

25,000 

50,000 

3 

20,000 

60,000 

4 

15.500 

62,000 

5 

12,100 

60,500 

6 

11,300 

67,800 

7 

9,300 

65,100 

8 

7,400 

59,200 

9 

6,500 

58,500 

10 

5,500 

55,000 

The  corresponding  curve  is  plotted  in  Fig.  68.  The  rapid  increase 
in  the  attractive  force  as  the  armature  approaches  the  poles  of  the 
magnet  is  shown  in  a  striking  manner. 

DISTANCES.    0*f345678910 


80,000 


70,000 


40,000 


30,000 


FIG.  68.     Ratio  of  Decrease  of  Magnetic  Attraction  to  Distance. 


Construction  of  Telegraph  Magnets.  91 

183.  Construction  of  Telegraph  Magnets. — Fig.  69  is  a 
representation  of  an  electro-magnet,  such  as  is  usually  employed  in 
telegraphy.  The  drawing  is  the  actual  size  and  proportions  of  a 
type  of  magnet  largely  used  by  some  of  the  most  successful  Ameri- 
can instrument-makers.  The  iron  portion  of  the  magnet,  of  the  best 


FIG.  69.    Telegraphic  Electro-Magnet—Full  Size. 

Swedish,  Norwegian,  or  Lowmoor  soft  iron,  consists  of  the  following 
parts:  (i)  the  core  proper,  which  is  cylindrical  in  form,  and  is  the 
part  around  which  the  wire  is  coiled :  it  is  made  in  two  parts,  A  A, 
usually  termed  the  legs  or  branches  of  the  magnet;  (2)  a  rectangu- 
lar bar,  B,  which  serves  to  unite  the  two  parts  of  the  core  (which  are 
secured  to  it  by  screws),  and  is  termed  the  yoke ;  and  (3)  the  arma- 
ture C,  which,  as  has  been  shown,  is  really  part  of  the  magnet,  being 
the  movable  portion  by  means  of  which  the  magnetic  force  is  exerted. 

184.  Theoretical  Proportions  of  Telegraph  Magnet— 
The  best  theoretical  proportions  to  secure  the  maximum  magnetic 
effect  from  a  given  quantity  of  current,  has  been  found  to  be  to  make 
the  four  parts  of  equal  length,  the  yoke  being  of  somewhat  greater 
cross-section  than  the  cores,  and  the  armature  of  equal  cross-section, 
but  broader  and  thinner  than  the  yoke.  But  inasmuch  as  quickness 
of  movement  is  one  of  the  most  important  considerations  in  tele- 
graphic apparatus,  experience  has  demonstrated  that  these  theoret- 
ical proportions  may  be  modified  with  practical  advantage. 

The  dimensions  and  proportions  of  the  iron  cores  of  electro- 
magnets have  been  the  subject  of  numerous  experiments  in  order  to 
determine  the  most  favorable  conditions  in  respect  to  the  two  quali- 
ties essential  in  telegraphic  instruments:  (T)  maximum  attractive 


9- 


Tke  Laws  of  Electro-Magnetism. 


force  with  a  given  current,  and  (2)  quickness  of  action.  These 
properties  are  in  their  nature  antagonistic,  and  hence  it  is  necessary 
in  practice  to  sacrifice  to  a  certain  extent  the  first-named  desidera- 
tum in  order  to  more  completely  secure  the  second.  The  results  of 
the  investigations  referred  to  have  shown  that  the  outer  diameter  of 
the  coils  or  helices  ought  to  be  three  times  that  of  the  cylindrical 
cores,  and  that  the  length  of  each  coil  or  helix  should  be  equal  to 
its  diameter.  These  proportions  are  exemplified  in  Fig.  69,  and 
approximate  closely  to  those  most  commonly  used  at  the  present 
day  in  the  United  States.  The  magnetic  intensity  developed  in  the 
iron,  within  certain  limits  elsewhere  set  forth  (174),  being  propor- 
tional to  the  quantity  of  current  traversing  the  wire  (measured  in 
amperes),  and  also  to  the  number  of  convolutions  or  turns  of  the 
wire,  we  may  express  the  magnetism  developed  in  the  iron  as  a  cer- 
tain number  of  ampere-turns. 

185.  Effect  of  Position  of  Windings. — It  makes  no  appre- 
ciable difference  upon  what  portion  of  the  core  any  particular  turn  is 
wound,  nor  does  the  fact  that  some  of  the  turns  may  be  close  to  the 
iron  and  others  at  a  greater  distance  from  it,  appreciably  modify  the 
result,  within  the  limits  of  the  dimensions  of  the  magnets  used  in 
telegraphy. 

186.  The   Helix  or  Coil. — Upon  the  cylindrical  cores  of  the 
magnet  are  fixed  flanges  or  collars  D  D  (Fig.  69),  of  hard  rubber  or 
other  like  material,  which,  in  connection  with  the  cores,  form  spools 
or  bobbins  upon  which-  the  magnetizing  coil  is  wound  in  superposed 
concentric  layers.      The  space  E  E,  which  is  designed  to  contain  the 
wire,  has  its  boundary  indicated  by  a  dotted  line. 

187.  Relation  of  Thickness  and   Length   of  Wire  to 
Number  of  Turns. — The  length  of  any  given  wire  which  can  be 


FIG.  70     Illustration  of  the  Law  of  Diametrical  Squares. 

wound  within  a  space  of  given  dimensions,  such  as  the  space  E  E, 
Fig.  69,  is  inversely  in  proportion  to  the  square  of  the  diameter  of 
the  wire.  This  will  appear  from  the  diagram  Fig.  70,  in  which  are 
shown  within  a  space  i  in.  square,  the  outlines  of  i  wire  i  in.  diame- 


Relation  of  Thickness  and  Length  of  Wire.     93 


ter,  4  wires  \  in.  diameter,  and  16  wires  J  in.  diameter,  all  of  which 
•occupy  precisely  the  same  area  of  cross-section  in  the  spool.  The 
number  of  turns  which  can  be  put  within  a  given  space  is  also  in- 
versely as  the  square  of  the  diameter  of  the  wire,  measured  to  include 
its  insulating  covering.16  As  the  electrical  resistance  of  a  wire  is 
•directly  as  its  length  and  inversely  as  its  sectional  area  or  the  square 
of  its  diameter  (118),  it  will  be  obvious  that  the  number  of  turns  in 
the  coil  of  any  electro-magnet  must  have  a  direct  and  invariable 
relation  to  its  resistance,  and  hence  the  resistance  of  a  coil  may  be 
taken  as  a  measure  of  the  number  of  turns  of  wire  it  contains.  This  is 
•convenient  in  practice,  inasmuch  as  the  resistance  is  easily  deter- 
mined by  proper  apparatus,  while  it  is  not  so  easy  to  find  the  number 
of  turns  in  a  coil  after  it  has  been  wound.  It  is  for  this  reason,  and 
not  because  the  resistance  in  itself  has  anything  to  do  with  the  mat- 
ter, that  it  has  become  customary  among  telegraphists  to  classify 
electro-magnets  by  reference  to  their  measured  resistances. 

It  is  difficult  to  wind  a  mag- 
net coil  neatly  and  accurately 
without  the  aid  of  machinery. 
It  may  be  done  in  a  common 
.lathe,  but  amateurs  generally 
will  find  it  more  convenient  to 
use  one  of  the  little  machines 
now  made  for  the  purpose, 
such  as  that  shown  in  Fig.  71. 
The  hub,  which  is  seen  lying 
on  the  table,  is  screwed  into 
the  end  of  the  cylindrical  core 
upon  which  the  coil  is  to  be 
wound,  and  its  other  end 
screws  on  the  spindle  at  the 
top  of  the  machine.  The  oper- 
ation of  winding  is  sufficiently 
explained  by  the  illustration." 

188.  Dimensions  and  Resistances  of  Magnet  Wires.— 

The  following  table  gives  the  properties  of  the  different  sizes  of  cop- 

18  A  very  convenient  rule  for  calculating  the  windings  of  the  coils  of  two  different 
electro-magnets  of  the  same  type,  but  of  different  dimensions,  is  given  by  Sir  William 
Thomson,  and  is  as  follows:  Similar  iron  cores  similarly  wound  with  lengths  of  wire 
proportional  to  the  squares  of  their  linear  dimensions  will,  when  excited  by  equal  cur- 
rents, produce  equal  intensities  of  magnetic  field  at  points  similarly  situated  in  with 
respect  to  them.  Professor  Silvanus  Thompson  has  also  pointed  out  as  a  corollary  that 
similar  electro-magnets  of  different  dimensions  must  have  ampere-turns  proportional 
to  their  linear  dimensions,  if  they  are  to  be  magnetized  up  to  an  equal  degree  of 
;saturation. 

"  These  machines  are  made  by  H.  Anderson,  Peekskill,  N.  Y. 


FIG.  71.    Machine  for  Winding  Magnet-Helices, 


94 


The  Laws  of  Electro-Magnetism. 


per  wire  most  used  for  the  helices  of  galvanometers  and  telegraphic 
magnets.  It  is  taken  from  one  calculated  by  George  B.  Prescott, 
Jr.,  on  the  basis  of  Dr.  Matthiessen's  standard,  viz.  : 

i  mile  of  pure  copper  wire  of 


n. 


ohms  at  59.9°  Fahr.18 


TABLE    VIII. 
DIMENSIONS  AND  PROPERTIES  OF  COPPER  MAGNET  WIRES. 


DIAMETER 
MILS. 

AREA. 

WEIGHT  AND 
LENGTH. 

RESISTANCE  AT  75°  FAHR. 

5  o 

AMERIO 
GAUGE  > 

Bare 
Wire. 

Silk- 
covered 
Wire. 

Circular 
MilsM 

iMiU 
.001  in. 

Square 
in. 

rf2x.78S4 

Lbs. 
per 

1000 
Feet. 

Feet 
per  Lb. 

Ohms 
per  looo 
Feet. 

Feet 
per  Ohm. 

Ohms 
per  Lb. 

18 

40.3 

42.6 

1624.3 

1275.7 

4.91 

203.8 

6.39 

156.47 

1.30 

20 

32.0 

34-o 

I02I.5 

802.3 

3.09 

324.0 

10.16 

98.401 

3.29 

22 

25-3 

27-3 

642.7 

504.8 

1.94 

5I5.I 

16.15 

61.911 

8.32 

24 

20.1 

22.2 

404.0 

317.3 

1.22 

819.2 

25.69 

38.918 

2I.O5 

26 

15-9 

17.9 

254-0 

199-5 

.77 

1302.6 

40.87 

24.469 

35.23 

28 

12.6 

14.2 

159-8 

125.5 

.48 

2071.2 

64.97 

15-393 

I34.56 

30 

10.0 

II.6 

100.5 

78.9 

•30 

3294.0 

103.30 

9.681 

340.25 

32 

8.0 

9.0 

63.2 

49.6 

.19 

5236.6 

164.26 

6.088 

860.33 

34 

6-3 

7-3 

39-7 

31-2 

.12 

8328.3 

261.23 

3.828 

2175.50 

36 

5-0 

6.0 

25.0 

19.6 

.08 

13238.8 

415.24 

.     2.408 

5497-40 

The  thickness  of  silk-covered  wire  is  approximate  only  ;  it  varies  somewhat  with 
different  makers. 

The  figures  in  the  table  refer  to  a  single  covering  of  silk.  For  a 
double-covered  wire,  add  the  difference  between  the  figures  in  the 
second  and  third  columns  to  the  figures  in  the  third  column. 

189.  Thickness  of  Spaces  between  Turns  of  Wire.— 
The  thickness  of  a  covered  wire  or  of  its  covering  cannot  be  cor- 
rectly determined  by  the  process  of  direct  measurement  by  a  gauge 
(192),  though  it  may  be  approximated  by  the  careful  use  of  such  a 
micrometer  caliper  as  that  shown  in  Fig.  73.  The  most  accurate 
method  is  to  measure  the  longitudinal  space  occupied  by  a  number 
of  turns  when  closely  wound  upon  a  mandril  or  small  cylinder ; 
divide  this  length  by  the  number  of  turns,  and  from  the  quotient 
subtract  the  diameter  of  the  copper  wire  measured  by  the  microm- 
eter caliper,  and  divide  the  result  by  2,  which  will  give  the  thickness 
of  the  covering.19 

18  Electrician  and  Elec.  Eng.,  iv.  217. 

19  Helices  made  of  bare  copper  wire,  accurately  wound  by  machinery  in  such  a 
manner  as  to  leave  an  air-space  of  i  mil.  (.001  in.)  between  each  two  adjacent  turns, 
and  having  the  successive  layers  separated  by  thin  paper,  have  been  much  used  in  the 
United  Slates  with  very  satisfactory  results. 


Instruments  for   Gauging  Wire. 


95 


190.  American  Standard  Wire  Gauge. — Great  confusion 
formerly  existed,  both  in  this  and  other  countries,  in  respect  to  wire 
gauges,  designated  as  the  custom  is  by  progressive  numbers,  there 
having  been  almost  as  many  so-called  standards  as  there  were  differ- 
ent manufacturers.     The  Brown  &  Sharpe  Manufacturing   Co.,  of 
Providence,  R.  I.,  some  years  since  established  a  gauge  in  which  the 
actual    thickness    of    wires    designated    by    successive   numbers    is 
made  to  diminish  in  a  true  geometrical   progression.     Under  the 
name  of  the  American  gauge^  this  has  now  become  the  generally 
accepted  standard  in  this  country  among  manufacturers  of  copper, 
brass,  and  german-silver  wires,  and  it  is  this  gauge  that  has  been 
used  in  this  work,  unless  otherwise  specified.     This  standard  has 
not  as  yet  been  generally  accepted  by  manufacturers  of  iron  wires, 
such  as  are  used  for  telegraph  lines. 

191.  British   Standard  Wire   Gauge.— In  Great  Britain  a 
uniform  wire  gauge  has  been 

adopted  by  law,  and  is  now 
the  only  authorized  standard 
in  that  country  for  all  kinds 
of  wire.  The  table  on  p. 
112  covers  the  range  of  sizes 
ordinarily  employed  in  teleg- 
graphy. 

192.  Instruments   for 
Gauging     Wire.  —  For 
quickly      determining      the 
gauge  number  of  a  wire,  the 
ring-gauge,  Fig.  72,  is  very 
convenient.     It  consists  of 
a  circular  steel   plate,  hav- 
ing  slots   accurately  cut   in 
its  edge,  these  being  num- 
bered successively  from  5  to  33,  covering  the  range  of  sizes  of  wire 
used  in  telegraph  work.     The  smallest  slot  which  any  given  wire 

can  be  made  to  enter  shows  its 
gauge  number.  Fig.  720  shows 
another  form  of  gauge  conven- 
ient for  the  pocket,  in  which  the 
point  at  which  the  wire  lies  in 

FIG.  72,,.   Pocket  v-Gauge.  the  an£le  formed  by  the  sides  of 

the  slot   shows   the  correspond- 
ing number  on   the  graduated   scale  by  inspection.     The  little  in- 


FIG.  72.    Wire  Gauge— Ring  Pattern. 


§  g  °  NEW  STANDARD  WIRC  a*U8C 


96 


The  Laws  of  Electro-Magnetism. 


FIG.  73.    Micrometer  Caliper. 


strument  known  as  the  micrometer  caliper,  shown  of  full  size   in 

Fig-  73,  is  extremely  accurate 
and  convenient.  It  will  readily 
determine  the  thickness  not 
only  of  wire,  but  of  sheet-metal, 
paper,  or  the  like,  from  the 
fraction  of  a  mil  up  to  0.3  in. 

193.  Adaptation  of  Mag- 
nets to  Working  Currents. 
— If  we  assume  three  electro- 
magnets like  that  in  Fig.  68, 
having  spools  or  bobbins  of 

equal  capacity,  and  wind  them  with  three  different  gauges  of  wire 
(for  the  sake  of  illustration,  say  the  three  sizes  shown  in  Fig.  69)  ; 
for  each  turn  of  a  wire  i  in.  in  diameter  we  should  have  4  turns  of 
the  \  in.  and  16  turns  of  the  \  in.  wire.  Now,  if  we  send  a  current 
of  i  ampere  through  the  thinner  wire,  one  of  4  amperes  through  the 
medium-sized  wire,  and  one  of  16  amperes  through  the  thick  wire, 
we  should  find,  in  accordance  with  the  principle  stated  in  (176), 
that  the  magnetic  force  would  be  precisely  equal  in  each  of  the  three 
magnets.  This  would  be  true,  notwithstanding  the  difference  in 
strength  of  current,  and  of  thickness,  length,  and  resistance  in  the 
wire  of  the  helix,  because  the  number  of  ampere-turns  is  the  same  in 
each  case.  We  have : 


Diameter  of  Wire. 

No.  of  Turns. 

Current. 

Ampere-turns. 

1.  00 

I 

16 

16 

50 
25 

4 
16 

4 

I 

16 
16 

A  thorough  understanding  of  this  principle  enables  the  elec- 
trician to  determine  the  winding  of  his  electro-magnet  so  as  to  corre- 
spond with  the  characteristics  of  the  current  by  which  it  is  intended 
to  be  worked  ;  for  it  will  be  readily  seen  that  to  produce  a  given 
intensity  of  the  magnetic  field,  upon  which  all  magnetic  effects  de- 
pend, the  number  of  turns  in  the  coil  must  be  in  inverse  proportion 
to  the  number  of  amperes  of  current  traversing  the  magnetizing  coil. 

194.  Spectrum  of  the  Electro-Magnet. — The  action  of  the 
magnetic  forces  in  such  an  electro-magnet  as  that  delineated  in  Fig. 
68  can  best  be  studied  by  means  of  magnetic  spectra,  produced  in 
the  manner  described  in  (68).  Fig.  74  shows  the  spectrum  of  such 
a  magnet,  when  the  current  through  the  coils  is  barelv  sufficient  to 


Magnetic  Hysteresis. 


97 


support  the  weight  of  the  armature.  The  manner  in  which  the 
magnetic  circuit  (177)  is  forced 
to  complete  itself  through  the 
air,  in  passing  from  one  pole 
of  the  magnet  to  the  other,  is 
beautifully  shown  by  the  curv- 
ing of  the  lines  of  force.  When 
a  soft-iron  armature  is  placed 
in  the  field  parallel  to  the  polar 
surfaces,  as  shown  in  Fig.  75, 
the  greater  number  of  the  lines 
of  force  are  deflected  so  as  to 
pass  through  the  ar-  . 


mature  ;     and     such 


FIG.  74.    Spectrum  of  Telegraph  Magnet.— Kennely  and 
Wilkinson. 


being  the  case,  the 
armature  itself  nec- 
essarily becomes  a 
magnet  of  opposite  polarity,  whereupon  mutual  attraction  takes  place 
between  the  magnet  and  its  armature  in  the  direction  of  the  lines  of 
force  which  pass  between  them, 
just  as  if  the  lines  were  so 
many  stretched  India-rubber 
bands,  and  the  force  was  due 
to  their  contraction.  When 
the  armature  is  brought  into 
actual  contact  with  the  magnet 
so  as  to  magnetically  connect 
its  poles,  it  becomes  virtually  a 
closed  or  endless  core  like  Fig. 
'66,  and  the  external 
lines  of  force  in  the  jj" — »•  - 
air  disappear. 

195.  Magnetic 
Hysteresis. —When 
a  mass  of  soft  iron,  such  as  the  core  of  an  electro-magnet,  becomes 
enveloped  in  a  magnetic  field  (169),  an  appreciable  time  elapses 
before  it  acquires  the  maximum  intensity  of  magnetization  which  the 
field  is  capable  of  producing.  On  the  other  hand,  when  the  iron  is 
withdrawn  from  the  field,  or,  what  is  the  same  thing,  the  field  is 
withdrawn  from  the  iron,  the  latter  does  not  lose  its  magnetism  in- 
stantaneously ;  the  magnetism  falls  off  progressively  in  the  same 
way  in  which  it  increased,  and  in  almost  every  case  some  small 


FIG.  75.    Spectrum  of  Telegraph  Magnet  and  Armature. 


98  The  Laws  of  Electro-Magnetism. 

quantity  of  magnetism  will  remain  for  some  time,  and  possibly  for- 
ever, after  the  separation  of  the  iron  from  the  field.  This  is  termed 
remanent,  or  more  commonly  residual  magnetism^  In  some  brands 
of  cold-blast  charcoal  iron,  when  carefully  annealed,  such  as  Norwe- 
gian, Swedish,  and  Lowmoor  iron,  scarcely  a  trace  of  residual  mag- 
netism remains,  and  these  irons  are  therefore  preferred  in  the 
manufacture  of  magnet  cores.  Experiment  has  also  shown  that  the 
shape  of  the  core  is  no  less  important  than  its  quality,  and  that 
quickness  of  action  and  freedom  from  residual  magnetism  may  be 
best  secured  by  making  the  cores  as  short  as  possible.  These  con- 
ditions are  sufficiently  fulfilled  for  ordinary  purposes  in  the  propor- 
tions of  the  magnet  shown  in  Fig.  68,  p.  91. 

196.  Induction  of  a  Current  upon  Itself. — It  has  been 
stated  (151)  that  an  electric  current  traversing  a  conductor  has  the 
capacity  of  inducing  a  temporary  current  in  a  neighboring  con- 
ductor. This  phenomenon  manifests  itself  in  the  coils  of  an 
electro-magnet  in  such  a  way  that  its  effects  are  added  to  those  of 
hysteresis  (with  which,  however,  they  must  not  be  confounded),  so 
as  to  still  further  delay  the  magnetization  and  demagnetization  of 
the  iron  core.  These  inductive  effects  make  their  appearance  when 
the  inducing  current  is  either  increased  or  diminished,  but  not 

while  it  remains  steady.  Fur- 
ther, an  increasing  or  diminish- 
ing current  not  only  induces  a 
current  in  neighboring  conduct- 
ors, as  indicated  in  Fig.  76  (in 

FIG.  76.    Illustration  of  Current  Induction  be-  '        v  . 

tween  Parallel  Wires.  which  the  arrow  shows  the  di- 

rection of  the  inducing  current 
in  the  wire  A,  and  of  the  induced  current  in 
the  wire  B),  but  it  may  also  exercise  an  in- 
ductive action  upon  the  conductor  in  which 
it  flows.  In  a  wire  coiled  back  upon  itself,  as 
in  Fig.  77,  an  increasing  current,  flowing  in 
the  direction  of  the  arrow  between  A  and  B, 
tends  to  induce  a  current  in  the  opposite  di- 
rection between  C  and  D,  which  opposes  the 
original  current  and  delays  its  increase.  If.  ^  77^^oi  Seif-m- 
on  the  other  hand,  the  current  between  A  duction  m  Coiled  Conductor. 

20  This  effect  was  carefully  studied  some  years  since  by  Professor  J.  A.  Ewing,  who 
gave  it  the  name  of  hysteresis,  from  a  Greek  word  signifying  "  to  lag  behind,"  denning 
it  as  the  lagging  behind  of  changes  in  magnetic  intensity  to  changes  in  magnetizing 
force.  EWING  :  Researches  in  Magnetism,  Philosophical  Trans.  Royal  Soc.,  1885. 


Causes  of  Retardation  in  Electro-Magnets.      99 

and  B  is  diminishing,  it  tends  to  induce  a  current  between  C  and  D 
in  the  same  direction  as  itself,  and  this  prolongs  the  duration  of  the 
original  current  by  delaying  its  decrease.  As  the  wire  in  the  coil 
of  an  electro-magnet  is  placed  under  the  same  conditions  as  the  wire 
in  Fig.  77,  it  is  clear  that  both  the  magnetization  and  the  demag- 
netization of  its  core  will  be  retarded,  first,  by  the  self-induction  of 
the  coil,  and  second,  by  the  effects  of  hysteresis  in  the  iron.  Besides 
this,  the  presence  of  the  iron  enormously  increases  the  normal  self- 
induction,  because  the  rising  magnetization  induces  an  opposing 
e.  m.f.  in  the  wire,  upon  the  principle  explained  in  (78),  for  it  will 
obviously  make  no  difference  whether  the  field  be  created  about 
the  wire,  or  whether  it  be  moved  thither  from  some  other  point  in 
space.  The  sum  total  of  these  effects  is  termed  magnetic  inertia. 

197.  Magnet  Cores  must  not  be  Hardened.— After  the 
core  of  a  magnet  has  been  annealed,  it  is  very  important  that  it 
should  be  left  black,  and  no  attempt  be  made  to  brighten  it  up.     If 
it  be  filed,  or  touched  ever  so  little  with  a  cutting  tool,  it  will  be 
slightly  hardened,  and  will  be  certain  to  show  traces  of  residual 
magnetism  (195)  when  put  to  service.     For  the  same  reason  the 
armature  of  an  electro-magnet  should  never  be  permitted  to  hammer 
upon  its  poles. 

198.  Effect  of  Self-induction  and  Hysteresis  in  Tele- 
graph   Magnets. — A   series   of  experiments   conducted   by  an 
officer  of  the  U.  S.  Coast  Survey  has  shown  that  the  average  period 
of  time  required  for  a  well-proportioned  telegraph  magnet  to  release 
its  armature,  varies  from  0.003  second,  with  maximum  tension  of 
retracting  spring,  to  0.033  witn  minimum  tension.21    The  best  work- 
ing adjustment  would  be  midway  between  these  values,  that  is  to 
say,  0.015  second. 

199.  Other  Indirect  Causes  of  Retardation  in  Electro- 
Magnets. — It  has  been  stated  that  the  magnetism  developed  in  a 
given  mass  of  iron  depends  solely  upon  two  factors,  the  quantity  of 
current,  and  the  number  of  turns  of  the  conducting  circuit  around 
the  iron  (176).     It  has  furthermore  been  stated  that  the  quantity  oi 
current  traversing  a  circuit  in  turn  depends  solely  upon  the  e.  m.j 
of  the  generator  and  the  resistance  of  the  conductor  (127).     But  ex 
periment  shows  that  in  respect  to  quickness  of  magnetization  and 
demagnetization,  irrespective  of  absolute  intensity  of  magnetism,  il 
makes  a  very  great  difference  whether  an  exciting  current  of  equal 
quantity  has  been  produced  by  a  low  e.  m.f,  acting  through  a  small 
resistance,  or  by  a  high  e.  m.f.   acting  through  a  proportionately 

«  G.  W.  DEAN  :  Coast  Survey  Report,  1864,  p.  211. 


100 


The  Laivs  of  Electro-Magnetism. 


great  resistance ;  the  magnetic  actions  in  the  latter  case  being  far 
more  rapid  than  in  the  former.  This  effect  is  due  to  the  greater  re- 
sistance, which  in  the  latter  case  has  to  be  overcome  by  the  currents 
of  self-induction  set  up  in  the  coils  of  the  magnet,  which,  as  we  have 
seen  (196),  tend,  in  proportion  to  their  strength,  to  give  rise  to  mag* 
netic  inertia,  by  delaying  both  the  magnetization  and  demagnetiza- 
tion of  the  iron  core.  The  e.  m.  f.  which  tends  to  set  up  these 
opposing  currents  is  necessarily  of  equal  value  in  either  case,  as  it  is 
determined  by  the  quantity  of  current  in  the  coil  and  the  intensity 
of  magnetism  in  the  core  :  but  the  resistance  the  currents  are  obliged 
to  overcome  is  much  greater  in  the  second  case  than  in  the  first,  and 
therefore  the  currents  themselves  are  in  fact  very  much  weaker,  and 
their  retarding  effect  is  diminished  in  the  same  proportion.  This  fact 
has  an  important  bearing  upon  the  working  of  fast-speed  instruments. 

200.  Electro-Magnet  with  Polarized  Armature.— If  the 
armature,  like  the  core  of  the  magnet,  is  of  soft  iron,  and  placed 
parallel  to  the  polar  surfaces,  as  in  Figs.  69  and  75,  the  action  is 
simply  one  of  attraction,  irrespective  of  the  polarity  of  the  magnet, 
and  independent  of  the  direction  of  the  exciting  current.     Jf,  how- 
ever, the  armature  itself  be  a  permanent  magnet  (63),  the  direction 
in  which  it  tends  to  move  will  depend  upon  the  polarity  of  the  elec- 
tro-magnet, which  in  turn  is  determined  by  the  direction  of  the  ex- 
citing current. 

201.  In  illustration  of  this,  let  the  electro-magnet  of  Fig.  78  be 
provided  with  a  polarized  armature,  consisting  of  a  small  permanent 
magnet  n  s,  which  is  pivoted  at  one  end  to  the  yoke  of  the  electro- 
magnet, while  its  opposite  end  is  free  to  play  back  and  forth  between 


Electro-Magnet  with   Polarized  Armature. 


the  poles  of  the  N  S  of  the  electro-magnet.  When  the  current 
passes  in  one  direction,  as,  for  example,  in  Fig.  78,  the  n  pole  of  the 
polarized  armature  is  attracted  by  the  unlike  pole  S  of  the  electro- 
magnet, and  at  the  same  time  repelled  by  its  similar  pole ;  but  upon 


Permanent  and  Electro-Magnets.  101 

the  reversal  of  the  direction  of  the  exciting  current,  the  polarity  of 
the  electro-magnet  is  likewise  reversed,  and  the  polarized  armature 
is  now  attracted  to  the  opposite  side,  as  shown  in  Fig.  79.  It  is  ob- 
vious, therefore,  that  the  direction  of  the  movement  of  the  polarized 
armature  depends  solely  upon  the  direction  of  the  current,  and  not 
upon  its  strength.  There  is,  therefore,  an  important  difference  be- 
tween the  operation  of  a  permanently  magnetic  or  polarized  arma- 
ture and  a  non-polarized  or  neutral  armature. 

202.  Combinations  of  Permanent  and  Electro-Magnets. 
— Various  mechanical  combinations  of  electro  and  permanent  mag- 
nets have  been  made,  all  of  which  involve  essentially  the  same  prin- 
ciples as  the  simple  apparatus  figured  above,  and  by  which  a  like 
effect  is  produced.  The  polarization  is  not  necessarily  confined  to 
the  armature,  as  similar  results  may  be  obtained  by  constructing  the 
apparatus  in  various  ways,  provided  that  some  one  portion  of  it  is 
polarized  and  another  portion  non-polarized.  This  principle  is  of 
special  value  in  multiple  telegraphy  (321). 


CHAPTER  VII. 

TELEGRAPHIC    CIRCUITS. 

203.  It  has  heretofore  been  explained  (30)  that  an  electric  circuit 
consists  of  an  endless  series  or  chain  of  conductors.     That  portion 
of  the  circuit  which  is  situated  between  the  terminals  or  poles,  and 
within  the  generator,  is  called  the  internal  circuit,  and  its  resistance 
is  the  internal  resistance  of  the  generator ;   the  chain  of  conductors 
which  joins  the  poles  outside  of  the  generator  is  called  the  external 
circuit,  and  its  resistance  is  the  external  resistance  of  the  circuit. 

204.  The  essential  characteristics  of  every  electric  circuit  are  the 
same,  although  such  a  circuit  may  vary  in  length  from  a  few  inches 
to  thousands  of  miles.      It  may  be  supplied  with  electricity  from  a 
single  source,  or  from   two   or  more   sources   situated   at  different 
points,  and  it  may  include  a  single  receiving  and  transmitting  instru- 
ment, or  a  large   number  of  such  instruments  situated  at  different 
points  along  its  course.     But  in  every  case,  without  regard  to  the 
length  of  the  circuit,  the  time  actually  occupied  in  the  transmission 
of  the   electric   impulses,  although   not   inappreciable,    may  be   re- 
garded, for  all  practical  purposes  of  ordinary  telegraphy,  as  instan- 
taneous. 

205.  Telegraphic  Circuits. — A  telegraphic  circuit  is  made  up 
of  the  following  parts  :  (i)  the  generators,  either  batteries  or  dynamo- 
electric  machines;   (2)  the  line  conductors;  (3)  the  earth,  which  is 
usually  employed  as  a  substitute  for  the  return  line  wire  from  the 
distant  station  ;  and  (4)   the  instruments  for  transmitting  and  receiv- 
ing signals. 

206.  Open    and    Closed    Circuits. — There   are   two  ways  in 
which  a  telegraphic  circuit  may  be  arranged  for  the  transmission  of 
signals,     (i)  The  generator  may  be  kept  normally  in  connection  with 
the  line,  thereby  causing  a  constant  current  to  traverse  the  circuit, 
and  signals  may  be  transmitted  by  alternately  breaking  and  closing 
the  circuit ;  or  (2)  the  generator  may  be  normally  disconnected  from 
the  line,  and  signals  may  be  transmitted  by  alternately  inserting  the 
generator  into  and  withdrawing  it  from  the  circuit,  so  as  to  cause  a 
current  to  flow  for  the  desired  period  of  time  to  form  the  signals. 

102 


Drawings  of  Electric  Apparatus.  103 

The  first  is  called,  in  a  general  way,  the  closed-circuit  and  the  second 
the  open-circuit  system.  In  other  countries  than  North  America  one 
or  the  other  of  the  above-mentioned  systems  is  almost  invariably 
employed,  but  the  system  in  universal  use  in  our  own  country, 
although  usually  spoken  of  as  a  closed-circuit  system,  may  more 
properly  be  regarded  as  a  compromise  between  the  two,  possessing 
some  of  the  characteristics  of  each.  As  in  the  true  closed-circuit 
system,  the  current  constantly  traverses  the  line  when  no  work  is  be- 
ing done,  but  signals  are  transmitted,  not  by  interruptions  of  this 
current,  but  by  first  interrupting  it  at  the  sending  point,  and  then 
transmitting  the  signals  by  closing  the  circuit  at  properly  timed 
intervals,  thus  permitting  the  current  from  the  generator  to  trav- 
erse the  line  and  the  receiving  instrument,  as  in  the  open-circuit 
system. 

207.  Drawings   of  Electric   Apparatus. — There  are  three 
principal  methods  of  representing  organizations  of  electrical  appa- 
ratus:   (i)  by  perspective  drawings,  (2)  by  geometrical  drawings,  and 
(3)  by  diagrams. 

Perspective  drawings  are  ordinary  pictorial  illustrations.  They 
show  the  appearance  of  the  apparatus,  but,  as  a  rule,  are  not  well 
adapted  to  convey  to  the  mind  a  clear  idea  of  its  principle  and  mode 
of  operation. 

Geometrical  or  working  drawings  consist  of  plans,  elevations,  or 
sections,  drawn  to  a  scale,  which  may  represent  the  whole  or  some 
part  of  the  apparatus.  They  usually  exhibit  all  the  constructional 
details,  whether  essential  to  the  operation  of  the  apparatus  or  not, 
and  while  indispensable  to  the  workshop,  are  ordinarily  of  little  use 
for  purposes  of  explanation.  Figs.  35  and  36  (pp.  46,  47)  are  exam- 
ples of-geometrical  drawings. 

Diagrams  exhibit  the  apparatus,  circuits,  and  connections,  not  in 
their  actual  form  and  proportions,  but  in  such  a  conventional  manner 
as  will  most  clearly  illustrate  the  principle  of  the  apparatus  and  its 
mode  of  operation.  Diagrams  ought  not  to  be  encumbered  with 
details  which  are  merely  constructional,  and  therefore  unessential. 
The  advantages  of  a  uniform  and  well-understood  system  for  the 
conventional  representation  of  electrical  apparatus  and  circuits  will 
be  apparent. 

208.  Conventional  Representations  of  Circuits  and  Ap- 
paratus.— In  the  following  paragraphs  are  briefly  described  various 
component  parts  of  telegraphic  circuits,  with  the  symbolical  repre- 
sentations which,  by  general  consent,  have  been  adopted  to  represent 
them,  and  the  apparatus  employed  in  connection  with  them. 


IO4  Telegraphic  Circuits. 

(1)  A  wire,  either  straight  or  curved,  connecting  two  points  in  a  circuit. 
Main  circuits  may  be  in  full,  and  local  circuits  in  dotted  lines,  where  such 
distinction  is  desirable. 

(2)  An  overhead  or  pole  line. 

(3)  A  submarine  or  subterranean  line  or  cable. 

(4)  The  point  at  which  any  branch  circuit  connection  is  made  is  indicated 
by  a  round  dot  at  the  intersection.     If  two  lines  cross  without  being  con- 
nected, the  dot  is  omitted. 

(5)  In  order  to  more  readily  distinguish  wires  which  cross  each  other  with- 
out electrical  connection,  it  is  usual   to  represent  a  loop  in  one  of  them  at 
ihe  crossing  point. 

(6)  The  direction  of  the  current,  from  positive  to  negative,  is  shown  by 
arrows. 

(7)  A  waved  line  denotes  an  artificial  resistance  or  rheostat  in  the  circuit. 

(8)  An  adjustable  rheostat. 

(9)  A  voltaic  cell  is  indicated  by  two  parallel  lines,  the  thick  line  repre- 
senting the  zinc  and  the  thin  line  the  copper. 

(10)  The  same  figure  arranged  in  the  reverse  way,  as  shown,  denotes  a 
storage  battery  or  accumulator. 

(n)  A  dynamo-electric  machine. 

(12)  A  ground  or  earth  plate. 

(13)  A  common  or  non-polarized  relay. 

(14)  A  polarized  relay. 

(15)  A  sounder. 

(16)  A  recording  instrument  or  register. 

(17)  A  galvanoscope  or  galvanometer.     If  a  tangent  galvanometer,  it  may 
be  represented  as  in  Fig.  50,  p.  65. 

(18)  A  coil  or  loose  bundle  of  wire,  its  use  being  indicated  by  a  reference 
letter. 

(19)  A  common  Morse  key. 

(20)  A  single-current  or  three-point  key. 

(21)  A  single-current  transmitter. 

(22)  A  double-current  transmitter. 

(23)  A  condenser. 

(24)  A  lightning  arrester. 

(25)  A  pole-changing  switch,  in  which  the  crosses  indicate  the  insertion 
of  plugs. 

(26)  A  universal  switch,  in  which  the  crosses  indicate  points  where  con- 
nections are  formed  by  inserting  plugs. 

(27)  A  three-point  switch. 

209.  The  Earth  as  an  Electrical  Conductor. — The  earth, 
being  composed  of  a  vast  mass  of  inorganic  material,  mostly  of  a 
porous  character,  and  permeated  throughout  by  water,  forms  an  ex- 
cellent conductor  of  electricity,  and  it  is  almost  invariably  employed 
in  this  capacity  as  a  part  of  every  telegraphic  circuit.  While  its 
specific  conductivity,  as  will  appear  from  the  table  (p.  57),  is  much 
lower  than  that  of  metallic  substances,  yet  this  is  abundantly 
compensated  for  by  the  enormous  area  of  its  cross-section. 


Representations  of  Circuits  and  Apparatus.      105 


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27. 


io6  Telegraphic  Circuits. 

Fig.  80  illustrates  the  principle  of  the  earth  circuit.  The  current 
of  the  battery  is  assumed  to  pass  through  the  earth  from  one  end  of 

the  line  to  the  other,  as  indi- 
cated by  the  arrow. 

210.  Ground  Connec- 
tion.— The  connection  with 
the  earth  is  made  by  means 
of  ground-plates,  which  may 
be  of  sheet  copper  -f$  in. 
thick,  and  having  an  area  of 

FIG.  80.     Diagram  of  Earth  Circuit.  36    by  48   in.        Plates  of  gal- 

vanized  iron  are  cheaperr 

and  are  often  used  instead  of  copper ;  they  appear  to  answer  the 
purpose  perfectly  well.  The  ground-plates  should  be  buried  in 
moist  earth  in  a  vertical  position.  In  many  cases  an  available 
substitute  may  be  found  by  attaching  the  terminal  of  the  line,  by 
soldering  or  otherwise,  to  a  pipe  which  forms  a  part  of  an  exten- 
sive network  of  gas  or  water  conductors  buried  in  the  earth,  the 
large  surface  of  which  insures  a  most  excellent  conducting  connec- 
tion. It  is  advisable,  wherever  possible,  to  attach  the  wire  to  both 
gas  and  water  pipes.  When  the  wires  are  thus  connected  to  a  pipe, 
certain  precautions  are  necessary  to  be  observed,  especially  that  of 
soldering  the  wire  to  the  pipe  outside  the  meter. 

The  connecting  wire  which  is  soldered  to  the  ground-plate 
should  be  coated  with  insulating  material,  to  prevent  corrosion 
of  the  wire  by  the  electrolytic  action  which  might  otherwise  take 
place  (27). 

If  circumstances  render  it  necessary  to  bury  a  ground-plate  in 
badly-conducting  soil,  as,  for  instance,  where  it  is  rocky,  sandy,  or 
gravelly,  without  sufficient  moisture,  a  pit  should  be  dug,  and  filled 
with  scrap  tin  or  other  waste  metals  laid  in  contact  with  the  plate, 
and  the  surface  drainage  and  discharge  from  water  pipes  should  be 
led  into  it. 

211.  Advantages  of  the  Earth  Circuit.— Several  important 
advantages  arise  from  the  use  of  the  earth  in  telegraphy  as  a  part  of 
the  circuit.  The  entire  cost  of  the  return  wire  and  its  insulation  is 
saved,  while  at  the  same  time  the  resistance  of  the  circuit  is  reduced 
nearly  one-half.  On  the  other  hand,  the  inclusion  of  the  earth  mate- 
rially increases  the  difficulty  of  maintaining  an  efficient  condition  of 
insulation  throughout  the  circuit  (219). 

The  specific  electrical  resistance  of  the  soil  and  of  the  strata  of 
the  earth,  due  to  the  geological  character  of  some  regions,  are  some- 


The  Open  Circuit.  107 

times  such  as  to  render  it  a  matter  of  great  difficulty  to  secure  a 
sufficiently  good  ground  connection. 

An  instance  was  observed  some  years  since  by  the  author  in  which  it  was 
impossible  to  secure  a  ground  connection  which  would  not  offer  an  abnor- 
mally great  resistance  to  the  flow  of  the  current.  This  was  in  the  anthracite 
coal  regions  of  Pennsylvania.  Professor  Moses  G.  Farmer  informs  him 
that  he  has  met  with  the  same  difficulty  in  some  places  in  the  mountainous 
districts  of  New  Hampshire  and  Vermont,  on  the  lines  between  Boston  and 
Montreal. 

212.  The  Open  Circuit. — A  telegraph  line  arranged  upon  the 
open-circuit  plan  is  illustrated  in  Fig.  81.  Two  terminal  stations 
are  shown,  each  having  a  battery,  a  transmitting  key,  and  a  receiving 
instrument.  The  circuit  of  the  line  divides  at  each  key  into  two 


_t± 


T- 


FIG.  81.    Diagram  of  Open-Circuit  System. 

branches,  of  which  only  one  can  be  closed  at  the  same  time.  One 
branch  includes  the  battery  only,  and  the  other  the  receiving  instru- 
ment only.  The  latter  branch  is  normally  in  connection  with  the 
circuit  of  the  line.  If  a  signal  is  to  be  sent,  the  key  is  depressed  by 
the  operator,  so  as  to  establish  the  connection  of  the  line  with  the 
battery,  having  first  broken  it  with  the  instrument.  A  current  from 
the  battery  will  now  flow  through  the  key  and  over  the  line  in  the 
direction  indicated  by  the  arrows  to  the  other  station,  where  it  passes 
through  the  instrument  contact  of  the  key  and  through  the  receiving 
instrument,  avoiding  the  battery,  and  thence  back  through  the  ground- 
plate  and  the  intervening  mass  of  earth  to  the  opposite  pole  of  the 
battery  at  the  sending  station,  thus  completing  the  circuit.  In  this 
arrangement,  therefore,  each  station  transmits  signals  by  inserting 
its  own  battery  at  timed  intervals  into  a  circuit  of  conductors  which 
is  already  complete. 


io8 


Telegraphic  Circuits. 


213.  The  Closed  Circuit.— Fig.  82  illustrates  the  closed-cir- 
cuit plan,  properly  so  called.  In  this  the  cells  of  the  battery  or  bat- 
teries are  always  in  the  line,  and  the  circuit  passes  normally  through 


FIG.  82.     Diagram  of  Closed-Circuit  System. 

the  rear  or  breaking  contact  of  the  keys,  and  through  the  receiving 
instruments  at  both  stations.  By  depressing  the  key  at  either  station 
(as  shown  at  the  right  hand  in  Fig.  82),  the  current  of  the  entire  line 
is  interrupted,  and  a  signal  is  simultaneously  given  upon  both  receiv- 
ing instruments  by  the  falling  off  of  the  armatures  of  the  electro- 
magnets of  the  receiving  instruments. 

214.  American    Modification   of  the    Closed    Circuit— 
Fig.  83  represents  the  American  modification  of  the  closed  circuit, 


FIG.  83.    Diagram  of  American  Modification  of  Closed-Circuit  System. 

which  is  the  standard  arrangement  employed  in  the  United  States, 
Canada,  and  Mexico.  It  differs  from  the  last  described  in  that  the 
circuit  does  not  normally  pass  through  the  key  at  all,  but  through  a 


Position  of  Battery  in   Closed  Circuit.       109 

switch  or  special  circuit-closer  beside  it,  which,  as  a  matter  of  con- 
venience, is  in  practice  usually  mounted  upon  the  key,  though  shown 
separately  in  the  diagram,  as  it  is  sometimes  arranged  in  fact.  To 
transmit  a  signal  according  to  this  plan,  the  circuit  of  the  line  is  first 
broken  by  opening  the  switch,  and  the  signals  are  then  made  by  de- 
pressing the  key  so  as  to  close  the  circuit  at  timed  intervals  upon  its 
front  contact-point.  As  in  the  last  case,  the  alternate  opening  and 
closing  of  the  circuit  at  one  station  affects  alike  the  receiving  instru- 
ments at  all  stations. 

215.  Comparative  Advantages  of  the  Different  Plans.— 
Each  of  the  foregoing  plans  of  organization  of  a  telegraphic  circuit 
has   certain   peculiar  advantages  and   disadvantages,  which  will   be 
further  considered  hereafter.     It  may,  however,  be  stated  here,  that 
one  principal  advantage  of  the  closed-circuit  systems  is  that  a  great 
number  of  stations  may  be  placed  upon  a  single  line  without  materially 
interfering  with  each  other,  and  may  be  equipped  with  the  simplest 
of  apparatus,  all  the  batteries  being  placed  at  the  terminal  stations, 
where   they  can  more    conveniently  receive   skilled    and   sufficient 
attention. 

216.  Position  of  Battery  in  Closed  Circuit.— While  it  is 
usual  in  a  closed-circuit  system  to  place  a  battery  at  each  end  of  the 
line,  as  shown  in  Figs.  82  and  83,  it  is  by  no  means  an  essential 
requirement.     Comparatively  short  lines  of  say  25  or  even  50  miles 
in  length  are  often  supplied  with  a  battery  only  at  one  end,  while 
very  long  lines  are  occasionally  provided  with  an  intermediate  bat- 
tery midway  between  the  terminal   batteries.      In  rare  instances  a 
battery  is  placed  in  the  middle  of  the  line  only.     The  arrangement 
shown  in  Figs.  82  and  83  is  considered  preferable  to  any  other?  unless 
for  exceptional  reasons  which  may  apply  to  some  particular  case. 

217.  General    Considerations    respecting    Telegraphic 
Circuits. — In  all  telegraphic   circuits  (with  the  exception  of  those 
of  direct  working  electro-chemical  systems,  which  do  not  come  within 
the  scope  of  this  work),  the  object  sought  to  be  obtained  is  to  pro- 
duce signals  at  a  distant  station  by  alternately  closing  and  breaking 
the  circuit  at  the  home  station,  so  as  to   alternately  magnetize  and 
demagnetize  the  electro-magnet  of  the  receiving  instrument  at  the 
distant  station.     It  is  therefore  primarily  essential  that  the  current 
traversing  the  coils  of  the  distant  electro-magnet  should  be  of  suf- 
ficient quantity  to  cause  the  latter  to  attract  its  armature  with  cer- 
tainty when  the  circuit  is  closed,  while,  on  the  other  hand,  it  should 
be  insufficient  to  maintain  the  armature  in  proximity  to  the  magnet 
against  the  force  of  the  antagonistic  spring,  or  other  retracting  device, 


no 


Telegraph  ic  Circu  its. 


when  the  circuit  is  broken.  This  result  is  most  perfectly  attained 
when  the  maximum  current  going  through  the  helix  of  the  receiving 
magnet  is  sufficient  to  cause  the  armature  to  be  promptly  attracted^ 
and  the  minimum  current  is  zero,  or  no  current.  But  upon  lines 
of  ordinary  length,  exposed  to  unavoidable  atmospheric  influences,, 
these  conditions  are  usually  impossible  of  fulfillment.  The  more 
nearly  this  ideal  condition  can  be  approximated  to,  the  better  are 
the  results.  It  can  only  be  fully  realized  upon  a  line  of  which  the 
insulation  is  absolutely  perfect. 

218.  Relation  of  Conductivity  to  Insulation  Resistance^ 
— Practically  the  end  aimed  at  in  all  telegraphic  circuits  should  be  to 
make  the  resistance  of  the  conductor  as  small  as  possible,  and  the 
resistance  of  the  insulation  as  great  as  possible.       Therefore,  in  con- 
structing a  telegraph  line,  it  is  important  to  employ  the  best  possi- 
ble conductor  which  the  necessary  limitations  of  cost  will   permit, 
and  to  prevent   the  escape  of  the  current   in  undesired  directions 
by  the  use  of  the  most  efficient  insulators. 

219.  Effect   of  Imperfect    Insulation. — The  deleterious  ef- 
fects of  imperfect  insulation  upon  the  operation  of  a  telegraphic  cir- 
cuit will  be  understood  by  reference  to  Fig.   84,  which  represents 


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i 

mm 

~H 

• 

! 

FIG.  84.    Effects  of  Imperfect  Insulation. 

two  stations,  A  and  B,  connected  by  a  telegraph  line,  the  earth 
being  used  as  a  return  conductor.  If  we  suppose  the  line  to  be 
provided  with  a  battery  at  station  A  only,  the  current  from  its  posi- 
tive pole  flows  along  the  line  toward  B,  as  indicated  by  the  arrows, 
but  a  small  portion  of  this  current  escapes  from  the  line  through  or 
across  the  defective  insulators  at  every  successive  support.  These 
currents  of  leakage  find  their  way  directly  into  the  earth  in  the  direc- 
tion indicated  by  the  arrows,  returning  to  the  negative  pole  of  the 
battery,  at  A,  without  going  through  the  instrument  at  B  at  all. 
Every  imperfectly  insulated  point  of  support  therefore  constitutes 


Telegraphic  Conductors.  1 1 1 

a  branch  circuit  (140),  and  causes  the  current  to  divide  in  pro- 
portion to  the  total  resistance  of  the  support  and  its  insulator  as 
compared  with  the  joint  resistance  of  that  portion  of  the  line  and 
the  branch  circuits  beyond  the  point  of  division.  It  is  evident 
that  the  greater  the  resistance,  jointly  and  severally,  of  the  insula- 
tors, and  the  less  the  resistance  of  the  line  conductor,  the  greater 
will  be  the  percentage  of  the  total  quantity  of  current  entering  the 
line  at  A  which  will  reach  the  instrument  at  B.  But  as  some  por- 
tion of  the  total  current  must  escape  from  the  line  at  every  point  of 
support,  it  will  come  to  pass,  unless  the  line  be  perfectly  insulated, 
that  at  some  distance  from  the  initial  point,  depending  both  upon  the 
conductivity  and  the  insulation  of  the  line,  so  large  a  proportion  of 
the  current  will  have  escaped  from  the  line  through  the  supports  to 
the  earth,  that  the  remainder  will  be  insufficient  to  produce  any 
appreciable  effect  upon  the  receiving  instrument. 

220.  Working  Efficiency  of  Telegraphic   Circuit. — The 
working  efficiency  of  a  telegraphic  circuit  is  therefore  determined  by 
the  ratio  between  the  resistance  of  the  conductor  and  the  resistance  of  the 
insulator.     If  the  total  resistance  of  the  conductor  be  divided  by  the 
total  resistance  of  the  whole  number  of  insulators — that  is  to  say,  by 
their  joint  resistance — the  quotient  will  represent  fas.  efficiency  of  the 
circuit.     The  smaller  this  quotient,  the  higher  the  efficiency  (243). 

221.  Telegraphic    Conductors.- — The   wires   used   for   tele- 
graphic conductors  are  almost  invariably  either  of  iron  or  of  copper. 
Iron  wires  were  formerly  exclusively  used  for  outside  or  aerial  lines. 
Since  1885  these  have  largely  been  superseded,  in  all  new  work,  by 
wires  of  hard  copper.      Copper  wires  are  invariably  employed  for  in- 
terior work,  which  term  comprises  the  wires  within  buildings  and 
about  the  apparatus.     They  are  also  employed  for  all  subterranean 
and  submarine  conductors.      The  table  on  page   112  gives  the  di- 
mensions, weight,  conductivity,  resistance,  etc.,  of  the  sizes  of  iron 
and   copper   wires    most   generally    employed    as   telegraphic   con- 
ductors. 

222.  Iron  AAfires. — Until  within  a  few  years   the  size  of  iron 
wire  most  commonly  employed  in  the  United  States  has  been  that 
known  as  No.  9,  which  probably  still  constitutes  something  like  one- 
half  of  the  total  mileage  of  the  country.     Nos.  8,  6,  and  4  are  larger 
sizes  which  have  come  into  use,  especially  since  1875.     No.  4  is  the 
largest  iron  wire  used  in  this  country,  and  No.  10  is  the  smallest 
used  in  the  public  telegraph  service.     These  numbers  refer  to  the 
so-called  Birmingham  gauge,  and  not  to  the  American   (190).     See 
Fig-  85- 


112 


Telegraphic  Circuits. 


TABLE     IX. 
SIZE,  WEIGHT,  AND  RESISTANCE  OF  TELEGRAPH  WIRES. 


EXTRA  BEST  BEST  GALVANIZED  IRON. 

(Washburn  &  Moen  Manufacturing  Company.) 

GAUGE 
No. 
W.&M. 

Diameter. 
Mils. 

Weight. 
Lbs.  per 
Mile. 

Resistance. 
Ohms  per 
Mile 

Feet 
per  Ib. 

Tensile 
Strength. 
Lbs. 

4 

229 

730                      7. 

7.23 

1900 

6 

196 

540                  9-5 

9-59 

1500 

8 

165 

380 

13- 

13.89 

1  100 

9 

I51 

320 

15- 

16.50 

900 

10 

138 

268 

18. 

19.70 

700 

ii 

123 

215 

23- 

24.65 

550 

12 

108 

164 

32. 

32.19 

450 

14 

83 

96 

55- 

55- 

150 

GALVANIZED  IRON. 

(British  Post  Office  Specifications.) 

GAUGE 
No. 

Diameter. 
Mils. 

Weight. 
Lbs.  per 
Mile. 

Resistance. 
Ohms  per 
Mile. 

Feet 
per  Ib. 

Tensile 
Strength. 
Lbs. 

.... 

242 

800 

6.75 

6.6 

2620 

.... 

209 

600 

9- 

8.8 

1960 

.... 

181 

450 

12. 

11.7 

1460 



171 

400 

13-5 

13-2 

1300 



121 

200 

27. 

26.4 

655 

HARD  DRAWN  COPPER. 

(John  A.  Roebling's  Sons  Company.) 

GAUGE 
No. 

Diameter. 
Mils. 

Weight. 
Lbs.  per 
Mile. 

Resistance. 
Ohms  per 
Mile. 

Feet 
per  Ib. 

Tensile 
Strength. 
Lbs. 

9 

114-43 

209 

4-3 

25.2 

625 

10 

101.89 

166 

5-4 

31-2 

525 

SOFT  COPPER. 

(Geo.  B.  Prescott,  Jr.) 

§  o      ^ 
3*      2    • 

AREA. 

WEIGHT  AND-         RESISTANCE  AT      0  FAHR. 
LENGTH. 

5    W         %~ 

I 

WO           C   ^ 

Circular 
Mils. 

Square 
Inches. 

Lbs. 
per  looo 
Feet. 

Feet        °hms 
Per  Ib.     P  p^ 

Feet        Ohms 
Ohm        perlb' 

10     101.9 

10381 

8153 

3L37 

31.38         I. 

looo       .0313 

12          80.8 

6260 

5128 

19-73 

50.69         1.59 

629       .0805 

14          64.1 

4107 

3147 

12.41 

80.59        2.59 

386       .208 

16       50.8 

2583 

2029 

7.8l 

128.14       4-02 

249      -515 

18       40.3 

1624 

1276 

4.91 

203.76      6.39 

156     1.302 

20         31.9             102  1 

802 

3-09 

324.15      10.16 

98    3.292 

Line  and  Office  Wires. 


1*3 


12 


In  the  construction  of  a  telegraph  line,  the  longer  each  bundle  or 
piece  of  wire  is  the  better,  so  long  as  it  does  not  exceed  a  weight 
which  is  convenient  for 
the  workmen  to  handle. 
Great  care  should  be  taken 
in  making  each  joint,  and 
in  any  case,  the  fewer 
joints  the  better.  A  loose 
and  poorly  made  joint 
sometimes  causes  as  much 
resistance  as  50  miles  of 
line. 

Fig.  86  shows  the  com- 
mon twist-joint  most  used 
in  the  United  States.  The 
ends  of  the  wires  are 
wrapped  tightly  around 
each  other  with  the  aid 
of  a  hand-vise  and  pliers, 
and  are  then  soldered,  to  insure  good  metallic  connection  and  to 
exclude  moisture.  The  usual  number  of  posts  or  supports  in  the 
United  States  is  from  30  to  40  per  mile.  The  smaller  the  number 
of  posts  the  less  the  leakage  from  imperfect  insulation  and  the  less 
the  cost. 


FIG.  85.    Iron  Wires  for  Telegraph  Lines— Actual  Size. 


FIG.  86.    Twist-Joint  for  Iron  Wire. 

223.  Office  \Vires. — The  copper  wires  used  for  interior  wiring 
should  generally  be  of  No.  16  American  gauge  or  thicker,  and  well 
covered  with  insulating  material.  If  the  location  is  perfectly  dry 
and  the  number  of  wires  is  not  very  great,  a  coating  of  cotton  braid, 
double,  and  saturated  with  paraffin  or  wax,  answers  very  well.  If 
there  is  any  danger  of  exposure  to  dampness,  some  of  the  higher 
grades  of  insulated  wire,  most  of  which  aie  known  by  special  trade 
names,  such  as  Kerite,  Okonite,  etc.,  are  to  be  preferred.  Specimens 
of  some  of  the  most  useful  varieties  of  these  office  wires^  as  they  are 
called,  are  illustrated  in  Fig.  87.  The  great  number  of  varieties  of 
insulation  now  in  the  market  offers  a  wide  scope  for  selection,  both 
in  quality  and  cost. 


Telegraphic  Circuits. 


BCD  E  F 

Fig.  87.    Insulated  Conductors  for  Interior  Construction. 


Reference 
Letter. 

Birmingham 
Gauge  No. 

Diameter  of 
Conductor. 
Mils. 

Material  of 
Insulation. 

Outside 
Diameter  of              Outer 
Insulation.           Covering. 
Mils.         : 

A 

16 

65 

Okonite 

148               Braided 

B 

18 

49 

Kerite 

120 

None 

C 

18 

49 

" 

165 

Braided 

D 

18 

49 

" 

1  20 

Lead 

E 

20 

35 

Okonite 

109 

None 

F 

20 

35 

Kerite 

95 

None 

G 

20 

35 

'  ' 

95 

Lead 

224.  Copper  Line  W^ires. — About  the  year  1880  it  was  dis- 
covered that  copper  wire,  drawn  by  a  process  which  gave  it  greatly 
increased  tensile  strength  without  materially  impairing  its  conduct- 
ing qualities,  could  be  had  in  the  market,  and  as  a  result  many  lines 
have  since  been  built  with  this  wire,  with  the  most  satisfactory  results. 
At  the  prevailing  prices  of  copper  and  iron,  the  cost  of  the  copper 
line  is  little  if  any  more,  all  things  considered,  than  that  of  an  iron 
line  of  equivalent  conducting  capacity  ;  while,  if  very  great  conduc- 
tivity is  desired,  it  is  absolutely  necessary  to  resort  to  copper,  as  an 


Telegraphic  Line  Insulators. 


iron  wire  thicker  than  No.  4  is  so  heavy  as  to  be  almost  unmanage- 
able. 

225.  Telegraphic  Line  Insulators. — Telegraphic    lines    are 
carried  through  the  country  supported  usually  upon  wooden  posts, 
but  occasionally  upon  other  structures,  such  as  buildings,  bridges, 
etc.     These  supports  are  separated  at  intervals,  varying  on  different 
lines  from   150  to  300  feet,  or  from  20  to  40  per  statute  mile.     At 
each  point  of  support  each  wire  is  affixed  to  an  insulator,  the  office 
of  which  is  to  prevent,  so  far  as  possible,  the  escape  of  the  current 
from  the  line  through  the  support  to  the  earth,  in  its  endeavor  to  re- 
turn to  the  battery  by  the  shortest  route   (219).     Much   ingenuity 
has  been  expended,  and,  it  must  be  confessed,  with  very  unsatisfac- 
tory results,  to  devise  an  insulator  which  shall  be  capable  of  per 
manently  maintaining  its  non-conduct- 
ing  properties    during    continued    wet 

weather.  The  insulator  which  is  in 
most  general  use  in  North  America  is 
an  inverted  cup  of  pressed  glass,  mount- 
ed upon  an  oak  pin  which  forms  its  sup- 
port, as  in  Fig.  87,  the  line  being  se- 
cured to  its  side  by  a  tie  wire  which  lies 
in  a  circumferential  groove  surrounding 
the  insulator.  The  ordinary  glass  in- 
sulator is  a  device  which  has  little  to 
recommend  it  except  its  cheapness. 
Nevertheless,  there  is  much  to  choose 
between  the  different  forms  in  which 
the  glass  insulator  is  to  be  had.  Two 
models  in  common  use  are  shown  in 
diametrical  cross-section  in  Figs.  88 
and  89.  The  figures  are  one-half  the 
actual  size,  and  the  measurements  are 
given  in  the  drawings. 

226.  Defects  of  the  Glass  In- 
sulator.— The   glass   of  which  these 
insulators  are  composed  is  a  substance 
which,  as  regards  its   body,  is  a  suffi- 
ciently good  non-conductor  under  most 
circumstances ;    but    unfortunately,    in 

rainy  and  damp  weather,  especially  when  the  temperature  of  the 
atmosphere  is  rising,  its  entire  surface  becomes  coated  with  a  con- 
tinuous film  of  moisture.  This  watery  film  forms  a  conductor  at 


FIG.  87.     Glass  Insulator  on  Oak 
Bracket.     Model  of  1865. 


n6 


Telegraph  ic   Circu  its. 


FIG.  88.     Western  Union  Old  Insulator. 


every  support,  which  conveys  a  portion  of  the  current  from  the  con- 
ductor to  the  supporting  pin  upon  which  the  insulator  is  mounted, 

from  whence  it  finds  its  way 
into  the  ground,  or,  still  worse, 
into  some  other  parallel  and 
neighboring  wire.  Although 
water  is  a  comparatively  poor 
conductor  (116),  so  that  the 
quantity  of  current  which  es- 
capes at  any  one  point  is  in- 
considerable, yet,  when  we  con- 
sider that  on  a  line  500  miles 
long,  there  may  be  more  than 
20,000  such  points  of  escape, 
the  aggregate  loss  becomes  in 
practice  a  most  serious  matter. 
227.  Resistance  Influ- 
enced by  Form  of  Insu- 
lator.— Each  insulator,  there- 
fore, must  be  regarded  in  wet 

weather  as  a  conductor,  and,  as  such,  is  subject  to  the  same  law  as 

every  other  conductor ;  that  is,  the  resistance  which  it  will  oppose 

to  the  escaping  current  is  directly  in  proportion  to  the  length  of 

the  conducting  film  upon  its 

surface,  and  inversely  as  its 

cross-section  (118).     Hence 

the  length  of  the  insulating 

surface,  measured   from  the 

point  of  contact  of  the  wire 

to  the  point  of  contact  of  the 

supporting  pin,  must  be   as 

great  as   possible.     On  the 

other  hand,  it  is  obvious  that 

the  smaller  the  diameter  of 

the  insulator,  both  external 

and   internal,    the  narrower 

will  be  the  conducting  film, 

and  the  greater  its  resistance. 

Tested    by   this    rule,    it   will  FIG.  89.     Western  Union  Standard  Insulator. 

be  seen  that  the  pattern  illus- 
trated in  Fig.  89  must  be  better  than  that  shown  in  Fig.  88,  as  in  the 
first  the  actual  linear  distance  from  the  conducting  wire  to  the  sup- 


Hard  Rubber  and  Paraffin  Insulators.       i  i  7 


FIG.  90.     Hard  Rubber  Insu- 
lator.   (Batchelder.) 


porting  pin  (as  shown  by  the  heavy  outline)  measures  5.5  in.,  while 
in  the  second  it  is  only  4.3  in.  It  is  true  that  the  insulator,  Fig.  88,  is 
somewhat  smaller  in  diameter  than  the  other,  which  is  so  far  an  advan- 
tage ;  but,  on  the  other  hand,  a  comparatively  great  part  of  the  insu- 
lating length  of  the  latter  is  underneath, 
where  it  is  well  protected  from  the  direct 
action  of  the  falling  rain. 

228.  The  Hard-Rubber  Insulator. 
— Another  variety  of  line  insulator  more  or 
less  in  use  is  the  hard-rubber,  which  con- 
sists of  a  malleable  iron  hook  for  clamping 
and  holding  the  wire,  covered  with  a  mass 
of  vulcanized  rubber,  in  cylindrical  form, 
with  a  thread  cut  upon  its  exterior,  which 
is  screwed  into  a  block,  wooden  arm,  or 
other  convenient  support,  as  shown  in  Fig. 
90.  The  non-conducting  properties  of  vulcanized  rubber  have  been 
found  to  deteriorate  very  rapidly  on  the  surface  by  exposure  to  the 
weather,  and  hence  this  form  of  insulator  is  now  but  little  used 
except  for  short  lines  in  cities,  for  which  it  possesses  some  advan- 
tages by  reason  of  its  small  size, 
light  weight,  and  general  con- 
venience. 

229.  The  Paraffin  Insu- 
lator.—  Fig.  91  is  a  sectional 
view  of  the  paraffin  insulator, 
which  has  been  much  used  on 
the  railway  telegraph  lines  of 
the  United  States.  An  outer 
cylindrical  shell  of  cast-iron, 
open  at  its  lower  end,  has  ce- 
mented into  it  a  narrow-necked 
inverted  bottle  of  blown  glass, 
within  which  again  is  cemented 
an  iron  stem,  carrying  at  its 
lower  end  a  hook  for  support- 
ing and  clamping  the  wire. 
The  surface  of  the  cement,  both 
within  and  without  the  glass  bottle,  is  coated  with  paraffin  having 
a  melting-point  of  about  145°  Fahr.  The  iron  shell  is  inserted  into 
a  hole  bored  in  the  under  side  of  a  cross-arm,  which  last  is  bolted 
transversely  to  the  upright  post. 


FIG.  91.    Paraffin  Insulator.    (Brooks.) 


i8 


Telegraphic  Circuits. 


230.  The  Porcelain  Insulator.— The  insulator  shown  in  Fig. 
92  is  made  in  great  perfection  in  Germany,  and  is  extensively  used 
in  Europe,  Asia,  and  South  America,  but  not  in  the  United  States. 
All  things  considered,  it  is  perhaps  the  most  efficient  insulator  now 

known.  The  figure  is 
a  sectional  view  of  the 
best  form,  known  as 
the  double  bell.  The 
material  is  a  fine  and 
dense  porcelain,  per- 
fectly non-porous,  and 
white  in  color.  The 
glaze  covers  the  whole 
internal  and  external 
surface,  and  is  of  a 
pure  white  color.  The 
thread  is  smoothly 
formed  and  well-de- 
fined. The  supporting 
bracket  is  of  malleable 
iron,  having  an  upright 
cylindrical  stem,  and 
the  socket  is  packed 

with  hemp  and  linseed  oil  when  the  insulator  is  put  on.  A  straight 
iron  bolt  with  a  shoulder  is  used  with  a  cross-arm,  secured  by  a 
nut  screwed  on  the  under  side  of  the  arm. 

231.  Defective  Insulation  of  American  Lines.— The  most 
serious  defect  in  the  construction  of  the  telegraphs  of  the  United 
States  is  unquestionably  the  character  of  the  insulation.     Very  few 
of  the  lines  exhibit  any  material  improvement  in  this  particular  over 
those  constructed  forty  years  ago.      It    is    true    that    the  working 
efficiency  of  the  more   important  lines  has  been  greatly  increased 
during  the  period  which  has  since  elapsed,  but  the  improvement  is 
due  almost  wholly  to  the  use  of  conductors  of  lower  resistance,  and 
to  the  substitution  of  powerful  dynamo-electric  machines  in  the  large 
terminal  stations  for  the  voltaic  batteries  formerly  used.     The  effi- 
ciency of  the    less    important   lines    is    no   greater,   and,   in   many 
instances,  not  as  great,  as  it  was  twenty  years  since.     The  insulators 
almost  universally  employed,  as  pointed  out  in  (227),  are  deficient 
both  in  material  and  in  design.     In  addition  to  their  inherent  defects, 
there  are  usually  a  considerable  proportion  of  cracked  or  broken 
ones,  which  the  most  vigilant  inspection  cannot  wholly  prevent.     The 


FIG.  92.    German  Porcelain  Insulator. 


Effects  of  Climate  upon  Insulation.  119 

records  of  the  Western  Union  Company  show  that  about  6  per  cent, 
of  the  glass  insulators  on  its  lines  require  renewal  yearly.1 

232.  Effects  of  Climate'  upon  Insulation. — The  combined  effect  of  dirt 
and  moisture  upon  the  surface  of  insulators  is  very  deleterious.  Ordinary 
insulators  in  this  country  are  affected  proportionally  as  the  air  becomes 
charged  with  moisture.  In  the  winter  months  this  often  occurs,  and  is 
notably  the  case  when  the  ground  is  covered  with  melting  snow,  and  the 
rain  is  from  the  south.  Northeast  storms  begin  with  the  wind  from  the 
northeast.  Usually  the  wind  changes  to  the  east  and  south,  and  finally  it 
clears  up  with  the  wind  from  the  west  and  northwest.  During  the  portion 
of  the  storm  when  the  wind  is  from  the  southeast  and  south,  the  air  is  charged 
with  moisture  to  its  full  capacity,  or  total  saturation.  It  is  during  this  time 
that  the  ordinary  glass  insulator  is  most  affected.  When  the  storm  is  accom- 
panied by  the  wind  changing  in  the  other  direction,  that  is,  from  northeast  to 
north,  and  finally  to  northwest,  the  insulation  is  much  less  affected,  because 
the  atmosphere  is  seldom  charged  to  over  80  per  cent,  of  full  saturation. 
DAVID  BROOKS  :  The  Telegrapher,  xi.  73. 

Mr.  Brooks,  who  has  devoted  much  attention  to  the  investigation 
of  questions  relating  to  the  insulation  of  telegraph  lines,  has  remarked 
that  in  cities  in  which  the  fuel  principally  used  is  anthracite  coal,  the 
gas  which  is  formed  and  escapes  into  the  atmosphere  produces  a 
very  deleterious  effect  upon  the  surface  of  glass  insulators.  He 
found  while  during  rain,  insulators  in  the  country,  in  regions  free 
from  smoke,  give  a  resistance  of  60  to  100  megohms  per  insulator, 
in  the  city  under  the  same  conditions  of  weather,  the  resistance  falls 
as  low  as  4  to  6  megohms  per  insulator.  He  instances  a  line  in  the 
city  of  Pittsburgh,  a  locality  formerly  famous  for  the  quantity  of 
bituminous  coal-smoke  which  pervaded  its  atmosphere,  where  glass 
insulators  which  had  been  exposed  on  the  line  less  than  two  years 
were  so  coated  with  soot  that  they  gave  a  measured  resistance  of 
less  than  i  megohm  per  insulator.  Moses  G.  Farmer,  who  is  also 
excellent  authority  in  such  matters,  says :  "  I  presume  from  long 
experience  and  many  careful  tests,  made  in  the  worst  weather,  that 
9  megohms  will  be  above  the  average  value  of  three-quarters  of  the 
insulators  used  in  this  country,  in  the  Middle  and  Northern  States, 
in  long-continued  heavy  storms."2 

A  very  fair  idea  of  the  comparative  efficiency  of  some  of  the  different 
insulators  referred  to  in  this  chapter  may  be  gathered  from  the  report  of 
a  test  of  five  years  duration,  extending  from  March  I,  1868,  to  March  i,  1873. 
The  different  varieties^of  insulators  were  exposed  in  sets  of  10,  the  mean 
resistance  of  this  number  being  taken  in  each  test.  The  total  number  of 

1  PRESCOTT  :  Electricity  and  the  Electric  Telegraph,  302. 
3  The  Telegrapher,  \.  34. 


I2O 


Telegraphic   Circuits. 


measurements,  in    rain,  during   this  period  was  93.     The  results  were  as 
follows  : 


DESCRIPTION  OF  INSULATOR. 

Resistance                  Resistance  per  Mile 
per  Insulator.                   of  40  Insulators. 
Megohms.                              Ohms. 

Mean. 

Minimum.i         Mean. 

Minimum. 

I.  Western    Union    glass,     1865 
tvDe  (like  Fitr   87)  . 

8-3 

8.6 
28.3 

10,000. 

14.6 

24. 

2.6 

3- 

19. 
2,300. 

6.4 

3-5 

207,500 

215,000 

707,500 
2,500,000,000 

365,000 
600,000 

65,000 

75,000 

475,000 

57,777,777 

160,000 
87,500 

2.  Large   Varley,    brown    stone- 
ware  with   ebonite    covered 
pin  (Knglish  standard) 

3.  Berlin  porcelain,   double  bell 
(like  Fig.  92)  
4.  Brooks'  Paraffin  (like  Fig.  91). 
5.  Boston      screw-glass     (nearly 
like  Fig.  87,  but  with  internal 
screw-thread),  exposed  I  year 
6.  Western     Union    glass,    1871 
type  (nearly  like  Fig.  88),  ex- 
posed i  year 

The  tests  were  made  by  D.  Brooks  of  Philadelphia.     The  Telegrapher :  ix.  90. 

234.  Distribution  of  Potentials  in  Telegraphic  Circuits. 

—The  manner  in  which  the  varying  potentials  at  points  in  an 
electric  circuit  may  be  graphically  delineated  in  accordance  with 
Ohm's  law,  has  been  explained  in  (145).  The  application  of  this 
method  of  illustration  to  the  specific  conditions  of  a  telegraphic 
circuit  is  instructive,  as  it  enables  the  student  to  form,  as  it  were, 
a  mental  picture  of  the  electrical  condition  of  every  portion  of  the 
line  when  in  normal  condition,  or  when  affected  by  leakage  arising 
from  faults  and  defective  insulation. 

In  pointing  out  the  application  of  this  graphic  method  of  repre- 
sentation, to  a  telegraphic  circuit,  it  will  be  convenient  in  the  first 
instance  to  assume  the  circuit  to  be  perfectly  insulated. 

235.  Potentials  in  Perfectly  Insulated  Circuit.— If  a  bat- 
tery of  100  gravity  cells  in  series  be  connected  to  a  perfectly  insu- 
lated line  of  say  100  miles  in  length,  open  at  the  distant  end,  as 
shown  in  Fig.  93,  the  line  will  acquire  a  potential  throughout  its 
entire  length,  of  100  volts,  which  is  equal  to  the  e.  m.  /.  of  the  battery. 
This  will  be  the  case,  however  great  may  be  the  length  of  the  line. 

236.  If  now  the  distant  end  of  the  line  be  connected  to  the  earth, 
as  in  Fig.  94,  a  positive  current  will  traverse  the  line.      This  will 
not  affect  the  e.  m.  f.   of  the  battery,  which  remains   100  volts  as 


Potentials  in  Perfectly  Insulated  Circuit.     121 


before,  but  the  distribution  of  potentials  will  be  changed  in  every 
part  of  the  circuit.  The  distant  end  of  the  line  becomes  o  or  zero, 
being  the  same  as  the  assumed  potential  of  the  earth  with  which  it  is 


100  Cells 


100 


75 


50 


35    Miles     0 


EARTH 


F"ic.  93.     Insulated  Open  Circuit. 


directly  connected,  and  from  this  point  it  rises  gradually  and  uni- 
formly along  the  line  to  the  terminal  or  pole  of  the  battery;  at  which 
point,  as  we  shall  hereafter  see,  it  will  be  something  less  than  100 
volts.  Having  ascertained  the  actual  potential  at  this  or  any  other 


HI 

EARTH 


cioo 
D 


75 


FIG.  94.    Circuit  Grounded  at  Distant  End. 


EARTH 


point  on  the  line,  it  may  readily  be  calculated  for  any  other  point, 
for  in  a  circuit  of  uniform  resistance,  the  potential  varies  directly  as 
the  distance  from  the  zero  end  of  the  line  (145).  Thus  if  it  is 
known  to  be  80  volts  at  100  miles,  it  must  be  40  volts  at  50  miles, 


Positive  and  Negative  Potentials  in  same  Circuit. 

20  volts  at  25  miles,  and  so  on,  the  different  poten- 
tials   at    different    points   being   represented   by  the 
sloping  dotted  line  in  Fig.  94.     The  potential  which 
has  been  referred  to  is  positive,  but  the  law  is  of  course  the  same 
with  a  negative  potential,  which  is  a  potential  less  than  that  of  the 


<TEARTH 


122  Telegraphic  Circuits. 

earth.  An  example  of  this  is  given  in  Fig.  95,  which  represents 
two  parallel  insulated  lines  each  100  miles  in  length,  looped 
together  at  the  distant  ends.  The  middle  of  the  battery  c  z  is 
connected  to  the  earth  ;  and  this  point,  therefore,  acquires  a  poten- 
tial of  zero.  The  upper  half  of  the  battery  imparts  a  positive  poten- 
tial to  the  upper  line,  and  its  lower  half  a  negative  potential  to 
the  lower  line.  The  potential  falls  regularly  from  the  c  pole  of  the 
battery  to  o,  and  rises  regularly  from  the  z  pole  of  the  battery  to  o. 
If  a  wire  were  connected  between  the  earth  and  any  point  along  the 
length  of  the  upper  line,  a  current  would  flow  from  the  line  to  the 
earth,  the  quantity  of  which,  by  Ohm's  law,  would  be  in  proportion 
to  the  potential  at  that  point.  If  the  wire  were  connected  in  the 
same  way  to  any  point  on  the  lower  or  negative  line,  a  current  would 
in  like  manner  flow  from  the  earth  to  the  line.  In  the  illustration 
given,  it  will  be  observed  that  there  are  two  points  of  zero  potential 
where  it  changes  from  positive  to  negative,  one  in  the  middle  of  the 
battery  and  the  other  at  the  point  where  the  lines  are  looped.  This 
is  the  same  as  the  distribution  of  potentials  in  Fig.  57,  p.  71,  and 
illustrates  the  distribution  on  a  telegraph  line  like  that  represented 
in  Figs.  82  and  83,  p.  108,  in  which  there  is  a  closed  circuit  with 
a  battery  at  each  end,  these  constituting  electrically  one  battery 
united  with  the  earth  at  its  centre  precisely  as  in  Fig.  95.  Fig.  96 
represents  a  line  of  100  miles  connected  with  a  battery  having  an. 

100  Cells 

100  Miles 


EARTH 


FIG.  96.    Measurement  of  Potential  by  Auxiliary  Battery. 
EARTH 

e.  m.  f.  of  100  volts,  the  distant  end  of  the  line  being  to  earth.  If" 
the  free  pole  of  a  second  battery,  with  its  similar  pole  to  the  earth, 
be  now  connected  at  any  point  to  this  line  through  a  galvanometer, 
each  battery  will  tend  to  send  a  current  to  the  line.  If  the  batteries 
are  of  equal  potential,  and  attached  at  the  same  point,  the  needle 
will  be  deflected,  say  to  the  right.  If  now  the  number  of  cells 
and  consequently  the  e.  m.  f.  of  the  second  battery  be  gradually 
diminished,  a  point  will  soon  be  reached  at  which  no  current  will 
traverse  the  galvanometer,  and  its  needle  will  stand  at  zero.  When 


Determination  of  Potential  by  Calculation.       123 

this  condition  exists,  the  e.  m.f.  of  the  second  battery  is  equivalent 
to  the  potential  of  the  line  at  the  point  of  attachment.  The  e.  m.  f. 
of  the  auxiliary  battery  will  always  be  less  than  that  of  the  principal 
battery,  even  when  connected  quite  close  to  it  ;  while  as  we  recede 
from  the  battery,  the  number  of  cells  or  the  e.  m.  f.  required  to 
maintain  the  needle  at  zero  will  gradually  diminish,  till,  near  the 
remote  end,  even  a  single  cell  will  suffice  to  send  a  current  into  the 
line,  because  the  potential  at  that  point  is  approximately  zero. 

236.  Determination  of  Potential  by  Calculation.— The 
diagram,  Fig.  97,  illustrates  the  manner  in  which  the  potential  at 
any  point  on  a  perfectly  insulated  line  may  be  calculated,  when  the 


t 


c 

FIG.  97.    Calculation  of  Potential  from  e.  m.  f.  of  Battery. 

e.  m.  f.  of  the  battery  is  known.  Let  A  B  represent  a  battery  of  say 
100  volts,  and  let  B  C  be  an  insulated  line  of  any  length.  Let  the 
line  A  B  be  drawn  of  such  a  length  as  to  be  in  proportion  to  the 
internal  resistance  of  the  battery  (131),  and  let  the  length  BC  cor- 
respond, in  the  same  proportion,  to  the  resistance  of  the  line.  Let 
the  height  of  the  line  A  D  represent  the  e.  m.f.  of  the  battery.  The 
height  of  the  line  B  E  will  now  represent  the  potential  of  the  line  at 
its  junction  with  the  battery,  while  the  height  of  a  vertical  line,  or 
ordinate,  F  G,  will  represent  the  potential  at  any  other  point,  as,  for 
instance,  F.  The  potential  at  any  point  in  the  line  may  be  calcu- 
lated by  the  following  rule : 

As  the  aggregate  resistance  of  the  line  and  battery  is  to  the  resist- 
ance C  F,  measured  from  the  distant  end  of  the  line,  so  is  the  e.  m.f. 
of  the  battery  to  the  potential  at  a  given  point  (as  F) ;  or, 

A  C  :  F  C  : :  A  D  :  F  G. 

237.  Potentials  within  the  Battery.— The  distribution  of 
potentials  within  the  battery  follows  precisely  the  same  law.  Fig.  98 
shows  a  battery  of  4  cells  connected  to  a  line  of  infinite  resistance — 
that  is,  having  its  distant  end  open.  The  potentials  are  indicated  by 
the  upper  dotted  line,  and  are,  under  these  conditions,  equal  to  the 
e.  m.f.  at  each  point.  The  potential  rises  approximately  i  volt  at 
each  surface  of  contact  between  the  zinc  and  the  exciting  solution, 


124 


Telegraphic  Circu its. 


the    aggregate    potential    being   attained    in   the  fourth  cell  of  the 
series. 

238.   Fig.  99  shows  the  same  battery  connected  to  a  line  having 


3 

... 


r 

.1'  Jb  \\,  L 


\\,  \\t  \ 


FIG.  98.     Battery  Potentials  with  Open  Circuit. 


EARTH 


the  same  resistance  as  itself;  that  is,  the  resistances  of  the  internal 
and  the  external  circuits  of  the  battery  (203)  are  equal.  The  poten- 
tial at  the  end  of  the  line,  instead  of  being  4  volts,  is  now  o,  or  zero. 


•       EARTH  EARTH 

FIG.  99.    Battery  Potentials  with  Closed  Circuit. 

The  potential  at  other  points  in  the  circuit,  measured  in  volts,  is 
shown  in  the  diagram  by  corresponding  figures.  It  will  be  observed 
that  the  potential  falls  in  the  liquid  portion  of  each  cell  in  proportion 
to  the  resistance,  in  the  same  way  that  it  does  on  the  line. 

239-  Fig.  100  shows  the. same  battery  short-circuited,  that  is,  con- 
nected at  each  end  with  the  earth  by  a  wire  of  no  appreciable  resist- 
ance. The  potential  at  both  ends  of  the  battery  being  now  main- 


Potentials  in  Imperfectly  Insulated  Circuit.      125 

tained  at  zero,  the  potential  rises  within  each  cell,  as  in  the  previous 
examples,  the  maximum  point  of  potential  being  at  the  contact  of  the 
zinc  plate  of  each  cell  with  the  liquid,  irrespective  of  the  number  of 


EARTH  EARTH 

FIG.  100.    Potential  in  Battery  on  Short  Circuit. 


FIG.  101.    Potential  in  Cell  on 
Short  Circuit. 


cells  in  the  series.      Within  each  cell  the  potential  falls  as  before,  in 
proportion  to  the  resistance  of  the  liquid. 

240.  Fig.  101  shows  a  single  cell,  short-circuited  by  a  wire  a  b, 
which  is  supposed  to  be  so  thick  and  so  connected  to  the  earth  as 
to  maintain  both  plates  z  c  at  a  potential  of  zero.     In  this  case  the 
difference  of  potential  in  the  circuit  exists  only  within  the  liquid,  as 
shown  by  the  diagonal  dotted  line.      In  all  these  varied  examples  we 
find  the  distribution  of  potentials  conforming  strictly  to  Ohm's  law 
as  laid  down  and  illustrated  in  Chapter  V.  of  this  work.3 

241.  Potentials  in   Imperfectly  Insulated  Circuit. — The 
distribution  of  potentials  in  a   perfectly  insulated  circuit   has  now 
been  explained,  but,  as  a  matter  of  fact,  no  telegraphic  circuit  is 
ever  perfectly  insulated,   and   in   wet  and   unfavorable  weather  the 


FIG.  102.    Distribution  of  Potential  on  Leaky  Line. 

insulation    is  usually  so  defective    that  the   normal   distribution  of 
potentials  is  materially  modified. 

9  For  the  illustrations  and  explanations  of  the  distribution  of  potentials  in  tele- 
graphic circuits  given  in  the  foregoing  paragraphs  (234  to  240),  the  author  desires  to 
acknowledge  his  indebtedness  to  LATIMER  CLARK'S  Electrical  Measurement^  pp. 
14-23 ;  one  of  the  very  best  of  the  early  works  on  practical  telegraphy,  but  unfortu- 
nately long  since  out  of  print. 


126 


Telegraphic  Circuits. 


In  Fig.  102,  let  A  B  represent  a  telegraphic  line,  connected  at  A 
to  the  pole  of  a  generator,  the  e.  m.  f.  of  which  produces  at  that 
point  a  potential  represented  by  the  perpendicular  A  F.  If  there  is 
situated  at  b  an  escape  through  an  imperfect  conductor  of  known 
resistance,  the  fall  of  potential  between  F  and  b\  and  between  b' 
and  B,  may  be  determined,  provided  the  resistance  of  the  line,  A  b 
and  b  B  is  known,  inasmuch  as  it  will  be  in  proportion  to  the  resist- 
ance (144).  It  will  be  observed  that  the  fall  of  potential  is  greater 
from  A  to  b  than  from  b  to  B.  Fig.  103  shows  the  distribution  with 


fb  /c 

FIG.  103.    Distribution  of  Potential  on  Leaky  Line. 

two  such  points  of  escape  of  equal  resistance  at  b  and  c.  Fig.  104, 
in  like  manner,  shows  the  distribution  with  five  points  of  escape,  bed 
ef.  In  each  of  these  cases,  the  line  at  B  being  in  direct  connection 
with  the  earth,  the  potential  at  that  point  is  zero.  The  difference  of 
potential  between  each  two  successive  points  of  escape  becomes  less 
and  less  as  the  distant  extremity  of  the  line  is  approached,  and 
hence  it  follows  that  the  quantity  or  effective  strength  of  current  in 


FIG.  104.     Distribution  of  Potential  on  Leaky  Lines 

the  line  progressively  decreases  at  each  point,  but  that  the  decrease 
becomes  less  and  less  rapid  as  the  terminal  station  B  is  approached. 
In  an  ordinary  telegraph  line  the  number  of  points  of  escape  are 


Effect  of  Imperfect  Insulation  upon  Current.      1 2  7 


very  numerous,  being  necessarily  equal  in  number  to  the  points  of 
support,  and  hence  the  line  of  potential,  F  B,  becomes  a  polygon  of 
a  corresponding  number  of  sides,  or  in  fact  a  regular  curve. 

In  Fig.  104,  therefore,  if  the  potential  at  the  initial  point  of  the 
line  A  is  assumed  at  100  volts,  we  might  find,  for  example,  at  suc- 
cessive points,  &'  c'  d'  e'f,  the  following  potentials,  with  a  perfectly 
insulated  and  with  a  leaky  line : 


Potential  at  point. 

Insulated  Line. 
Volts. 

Leaky  Line. 
Volts. 

A 

100.00 

100.00 

b 

83.34 

81.8 

c 

66.68 

64.5 

d 

50.00 

47-8 

e 

33-33 

31.6 

f 

16.66 

15-7 

B 

o.oo                           o.o 

The  less  the  resistance  of  the  leaks,  or  the  greater  the  leakage  at 
each  point,  the  more  will  the  curve  F  B  of  potentials  vary  from  the 
normal  straight  line. 

242.  Effect  of  Imperfect  Insulation  upon  Flow  of  Cur- 
rent.— The  effect  of  imperfect  insulation  upon  the  line,  whether 
general  or  special,  is  to  largely  reduce  the  resistance  of  the  line,  and 
proportionately  increase  the  quantity  of  current  drawn  from  the  bat- 
teries by  the  line,  so  that  the  latter  are  exhausted  much  more  rapidly 
when  the  weather  is  wet.  Hence,  in  working  on  the  closed  circuit 
plan  (213,  214),  the  line  current  is  strongest  in  wet  weather,  except 
near  the  middle  of  the  line ;  but  the  variation  or  margin  at  any  sta- 
tion, when  the  key  is  alternately  opened  and  closed  at  another  sta- 
tion, which  constitutes  the  working  efficiency  of  the  line,  is  very  much 
diminished.  This  variation  or  difference  of  course  determines  the 
available  strength  of  signals.  The  effect  of  imperfect  insulation 
upon  the  transmission  of  the  current  to  a  distant  station  has  been 
referred  to  in  (219).  The  various  electrical  characteristics  of  leaky 
lines  have  been  found  capable  of  determination  by  mathematical 
analysis. 

Since,  however  good  the  insulator  may  be,  some  small  portion  of  the  cur- 
rent escapes  from  the  line  over  it  down  the  post  to  the  ground,  it  is  mani- 
fest that  if  the  line  be  long,  the  posts  many,  and  the  insulators  very  poor,  a 
small  portion  only  of  the  entering  current  may  reach  the  far  end  of  the  line. 

The  law  which  governs  this  may  be  thus  enunciated  :  If  the  current  upon 
the  line  near  the  battery  be  called  the  entering  current,  and  that  upon  the 
distant  end  near  where  it  enters  the  ground  be  called  the  arriving  current. 


128  Telegraphic  Circuits. 

then  the  distance  to  which  any  stated  fraction  of  the  entering  current  will 
reach  is  proportioned  directly  to  the  square  root  of  the  conductivity  of  the 
wires,  to  the  square  root  of  the  insulating  power  of  the  insulator,  and 
inversely  to  the  square  root  of  the  number  of  poles  per  mile  used.  MOSES 
G.  FARMER:  See  Report  on  Telegraphic  Apparatus  at  Paris  Exposition  (1867), 
by  S.  F.  B.  Morse,  p.  69. 

243.  Resistance  and  Current  in   Leaky   Lines. — When 
the  average  resistance  of  each  insulator  is  known,  it  is  easy  to  com- 
pute the  actual  insulation  of  the  line  per  mile,  or  other  unit  of  length. 
It  is  only  necessary  to  divide  the  resistance  of  a  single  insulator  by 
the  number  of  insulators,  inasmuch  as  it  is  simply  a  case  of  joint 
resistance  (134).      So  also,  when  the  resistance  per  mile  of  the  con- 
ductor, and  the  resistance  per  mile  of  the  insulation  are  both  known, 
the  apparent  resistance  of  the  conductor  and  of  the  insulation  for 
any  length  of  line  may  be  determined.      As  the  mathematical  com- 
putations in  this  case  are  somewhat  complex,  a  compilation  of  results 
•is  given  in  convenient  form  for  use,  in  Table  X,  p.  129.     This  table 
shows  the  apparent  conductivity  and  insulation  resistance  (as  meas- 
ured from  the  terminal  station)  of  various  lengths  of  leaky  line,  from 
100  to  2,500  units.    The  table  also  gives  the  percentage  of  any  given 
entering  current  which  will  reach  a  terminal  station  located  at  vari- 
ous distances  along  the  line.     Many  problems  arising  in  the  working 
of  leaky  lines  may  be  conveniently  solved  by  means  of  a  table  of  this 
kind.4 

In  a  well  insulated  line,  the  ratio  of  the  conductivity  to  the  insu- 
lation resistance  ought  to  be  as  low  as  i  to  80,000.  The  table  is 
computed  upon  an  assumed  ratio  of  i  to  10,000,  which  is  probably 
as  much  as  can  be  relied  on  in  rain  with  the  most  carefully  con- 
structed glass-insulated  lines  in  our  climate,  and  may  be  regarded  as 
fairly  representative  of  the  actual  present  practice. 

244.  Computation  of  Working  Efficiency  of  Line. — As  an 
example  of  the  use  of  this  table,  suppose  it  be  required  to  determine 
the  comparative  working  efficiencies  of  the  open-circuit  (Fig.  ST,  p. 
107)  and  the  closed-circuit  system  (Fig.  83,  p.  108)  on  a  line  of  200 
miles  in  length,  with   a  conductor  of  10  ohms  resistance  per  mile, 
supported  upon  40  poles  per  mile,  the  wet-weather  value  of  the  insu- 
lators being  4  megohms  each,  and  the  resistance  of  the  instruments 

4  The  author  desires  to  express  his  obligations  to  Professor  Moses  G.  Farmer  for 
valued  assistance  in  the  preparation  of  this  table.  The  formulas  and  methods  of  com- 
putation are  discussed  in  the  following  named  works :  J.  GAVARRET  :  Telegraphie 
Electrique,  376 ;  E.  E.  BLAVIER  :  Telegraphic  Electrique,  ii.  447,  449 ;  A.  B.  KEMPE  : 
On  the  Leakage  of  Submarine  Cables;  Jour.  Soc.  Tel.  Eng.,  iv.  90 ;  H.  R.  KEMPE: 
Hand-book  of  Electrical  Testing  (3d  ed.),  445. 


Resistances  and  Escape  upon  Leak**  Lines.      129 


TABLE     X. 
RESISTANCES  AND   ESCAPE   UPON   LEAKY  LINES  OK  VARIOUS  LENGTHS. 

[The  unit  of  this  table  is  that  length  of  any  line  of  which  the  ratio  of  the  con- 
ductivity to  the  insulation  resistance  is  as  i  :  10,000.] 


True  Conductivity 
Resistance. 
Line  to  Ground. 
Units. 

Apparent  Conduc- 
tivity Resistance. 
Line  to  Ground. 
Units. 

Apparent  Insulation 
Resistance. 
Line  open. 
Units. 

Per  cent,  of  Enter- 
ing Current  reaching 
grounded  end  of  Line 
of  Resistance  as  in  first 
Column. 

100 

99.6 

10030 

99-5 

200 

197.2 

5060 

98. 

300 

291. 

3430 

95-7 

400 

379-3 

2630 

92.5 

500 

461. 

2160 

88.7 

600 

535-6 

1850 

84.4 

700 

602.  5 

1630 

79-7 

800 

662. 

1480                             74-7 

900 

712. 

1380 

69.7 

1OOO 

760. 

1300 

64.8 

1  100 

798. 

1250 

59-9 

J20O 

830. 

I2IO 

55-2 

1300 

857; 

1180 

50-7 

14OO 

880. 

1150 

46.5 

1500 

900. 

1130 

42.5 

I6OO 

916. 

1  1  10 

38.8 

I7OO 

930. 

1090 

35-3 

l800 

942. 

1070 

32.2 

IOXX) 

950. 

1060 

29.2 

2OOO 

960. 

1050 

26.6 

2IOO 

967. 

1040 

24.1 

22OO 

974- 

1030 

21,9 

23OO 

979- 

1024 

19.9 

24OO 

983. 

1018 

16.8 

2500 

987- 

1013 

14.7 

Infinite 

1000. 

1000 

oo. 

130  Telegraphic  Circuits. 

ioo  ohms  each.  This  would  give  for  the  line  the  same  ratio  of  con- 
ductivity to  insulation  as  that  assumed  in  the  table,  viz:  i  :  10,000. 
The  true  conductivity  resistance  of  the  line  from  A  to  B  (Fig.  105)  is 
2000  ohms.  Assume  the  keys  to  be  closed  at  both  stations,  the 


•-*-...  o 


FIG.  105.     Distribution  of  Potentials  upon  Leaky  Line  (Closed) 


resistances  of  both  instruments  being  alike,  the  e.  m.  f.  of  the  two 
batteries  also  equal,  and  the  internal  resistance  of  the  batteries  to  be  so 
small,  compared  with  that  of  the  line,  that  it  may  be  neglected.  The 
first  half  of  the  line,  from  A  to  o,  will  be  positive,  and  the  other  half, 
from  o  to  B,  negative.  When  sending  to  A,  the  key  at  B  is  alter- 
nately open  and  closed. 

When  key  at  B  is  open,  the  entire  length  becomes  positive,  being 
wholly  charged  from  the  positive  pole  of  battery  at  A  (Fig.  106). 


IDW'I'h 


FIG.  106.     Distribution  of  Potentials  upon  I  eaky  Line  (Open). 


With  both  keys  closed,  if  a  galvanoscope  were  to  be  connected 
between  the  point  o  and  the  earth,  it  would  indicate  no  current, 
because  the  potential  at  o  is  zero.  Hence  the  quantity  of  current 
going  to  line  from  the  battery  at  A  will  be  the  same  as  if  the  line  were 
connected  to  the  ground  in  the  middle — that  is,  at  a  point  ioo  miles  from 
A.  Assuming  the  e.  m.f.  of  the  battery  to  be  TOO  volts,  the  quantity 
of  current  entering  the  line  at  A,  by  Ohm's  law,  will  be  as  follows : 

With  key  closed  at  B  : 

Apparent   resistance  of  ioo  miles  (1000  ohms)  of 

leaky  line  (as  per  Table  X.) 760  ohms 

Resistance  of  instrument  at  A ioo      " 

860      " 
Quantity  of  current  ioo  (volts)  -?-  860  (ohms)  =  .1163  (amperes). 


Effect  of  Position  of  Fault.  131 

With  key  open  at  B  : 

Apparent  resistance  of  200  miles  (2000  ohms)  of 

leaky  line  (Table  X*.) 1050  ohms 

Resistance  of  instrument  at  A 100     ' ' 

1150     " 
Quantity  of  current  100  (volts)  -*-  1150  (ohms)  =  0.087  (amperes). 

Thus  we  have  : 

Current  in  line  at  A  when  B  is  closed 1 163  amperes. 

Current  in  line  at  A  when  B  is  open 0870         " 


Net  efficiency  of  circuit 0293         " 

Considering  next  the  open-circuit  plan,  in  which  the  instrument  at 
the  sending  station  is  cut  out  by  the  key  while  the  signalling  current 
is  entering  the  line  : 

With  key  closed  at  B  : 

Apparent  resistance  of  200  miles  of  leaky  line  +  instru- 
ment at  A  (100  ohms)  =  2100  ohms 967  ohms 

Quantity  of  current  entering  line  200  (volts)  -f-  967  ohms 
=  0.206  amperes. 

By  fourth  column  in  Table  X,  26.6  per  cent,  of  this  only  will  reach  the 
instrument  at  A  : 

26.6  per  cent,  of  .206  is  .0548.     Hence  : 

Current  in  line  at  A  when  B  is  closed 0548 

Current  in  line  at  A  when  B  is  open oooo 

Net  efficiency  of  circuit °548 

245.  This  investigation  shows  that  on  a  defectively  insulated  and 
leaky  line,  a  material  advantage  is  gained  by  dispensing  with  the 
battery  at  the  receiving  end  of  the  line,  and  assembling  it  all  at  the 
sending  end.     In  the  case  under  consideration  the  difference  in  effi- 
ciency with  the  same  line  and  instruments  is  as  548  to  293  in  favor 
of  the  open  circuit  plan.     With  the  battery  constantly  on  the  line,  a 
computation  may  be  made  by  the  aid  of  the  table,  which  will  show 
that  it  makes  no  difference  in  the  working  efficiency,  whether  the 
battery   be   placed    in   equal   amount   at  each    terminal    station,   or 
whether  it  be  all  assembled  in  the  middle  of  the  line.5 

246.  Effect  of  Position  of  Fault.— The  detrimental  effect  of 
a  special  defect  in   insulation  or  cause  of  escape,  such  as  contact 
with  the  branch  of  a  tree  or  a  wet  roof,  is  greatest  when  it  is  situated 

s  CROMWELL  F.  VARLBY  :  Report  on  Lines  of  Western  Union  Telegraph  Co.  (Ms.), 
1867. 


132  Telegraphic  Circuits. 

midway  between  the  terminal  stations  of  the  line,  assuming  the  bat- 
teries and  instruments  to  be  alike  at  each  end. 

When  the  fault  is  nearer  one. end  of  the'line,  the  station  farthest 
from  it  will  receive  the  weakest  signals,  and  the  station  nearest  it  the 
strongest  signals. 

In  increasing  the  battery  power,,  in  order  to  work  over  a  special 
defect  or  fault  in  insulation,  the  addition  should  be  made  to  the  sta- 
tion nearest  the  fault. 

247.  Best  Position  of  Batteries  in  Circuit. — If  the  insu- 
lation of  a  line  were  perfect  at  all  times,  the  position  of  the  battery 
in  the  line  would  be  immaterial.     As  all   lines  are  ordinarily  subject 
to   more  or   less  escape   or  leakage    throughout   their  length,  it   is 
obviously  not  advisable,  except  upon   comparatively  short   lines,  to 
place  all  the  battery  at  one  end ;  for  in  such  case  the  signals  will  be 
received  with  much  more  difficulty  at  the  station  where  the  battery  is 
situated,  than  at  the  opposite  end  of  the  line.     The  usual  arrange- 
ment of  a  battery  at  each  end  is  altogether  preferable. 

248.  Intermingling  of  Currents  on  Different  Lines. — The 
escape  of  the  current  through  the  insulators,  poles,  and  cross-arms 
from  one  wire  to  another  'n   wet  -weather,  known  as  cross-fire,  is  a 
far  more  prolific  cause  of  interference  in  the  working  of  lines  than 
the  mere   leakage  to  ground.      This  effect  is  sometimes  miscalled 
induction.     Weather-cross  is  perhaps  a  more  appropriate  term. 

As  electric  currents  always  flow  in  greatest  quantity  in  the  direc- 
tion of  the  least  resistance,  the  tendency  is  for  the  currents  to  escape 
from  a  long  circuit  into  a  short  one,  or  from  a  wire  of  higher  into 
one  of  lower  resistance.  A  simple  escape  to  ground,  if  not  too 
serious,  may  be  overcome  by  the  judicious  application  of  increased 
battery-power  ;  but  when  transverse  leakage  or  cross-fire  exists 
between  different  wires  running  upon  the  same  line  of  poles,  any 
attempt  to  increase  the  battery,  in  order  to  improve  the  working  of 
one  wire,  produces  a  detrimental  effect  upon  the  working  of  all  the 
others  parallel  to  it.  Upon  the  occurrence  of  a  sudden  shower,  the 
effects  of  cross-fire  are  usually  manifested  sooner  than  the  escape  to 
ground,  because  the  horizontal  cross-arms  are  wet  and  become  par- 
tial conductors  sooner  than  the  vertical  pole. 

249.  Remedy   for  Cross-Current.—  This  difficulty  may   be 
overcome  by  attaching  a  ground  wire  to  each  pole,  the  upper  end  of 
which  is  wrapped  around  the  central  portion  of  each  arm.     These 
wires  act  to  intercept  the  currents  of  leakage  passing  from  one  wire 
to  another,  and  to  convey  them  to  the  earth.     The  battery  may  then 
be  increased  as  much  as  desired  on  any  one  wire  without  interfering 


Value  of  Poles  and  Cross-Arms  as  Insulators.     133 

with  the  others.  It  is  true  that  the  pole,  even  when  wet,  has  some 
little  value  as  an  insulator,  which  is  lost  by  this  appliance,  but  the 
gain  in  the  other  direction  much  more  than  compensates  for  it. 

250.  The  results  of  defective  insulation,  in  causing  the  mixture  of 
currents  between  different  wires  on  the  same  line  of  posts,  are  much 
more  detrimental  near  the  ends  of  the  circuits  than  in  the  middle 
portions  ;  and  as  the  terminals  of  the  lines  are  almost  invariably  in 
large  towns  and  cities  where  the  insulation  is  usually  much  worse 
than  elsewhere  (232),  the  evil  is  aggra- 
vated   accordingly.      Much     would     be 

gained,  therefore,  by  applying  ground- 
wires  to  the  poles  even  for  a  distance 
of  25  miles  out  from  each  terminus. 

251.  Value  of  Poles  and  Cross- 
Arms  as   Insulators.— Tests  made 
many  years  since  to  determine  the  aver- 
age resistance,  in   wet   weather,  of  the 
pin-and-glass  insulator,   the    cross-arm, 
and   the   pole   respectively,   gave    some 
interesting  results.    The  tests  were  made 

from  New  York  to  Philadelphia  (99  miles),  and  to  Boston  (236 
miles).  The  following,  in  connection  with  Fig.  107,  will  explain  the 
method  employed : 

Let  a  =  the  resistance  of  half  the  arm. 

Let  b  =  the  average  resistance  of  the  insulator  and  supporting  pin. 

Let  c  =  the  resistance  of  the  pole. 

The  following  measurements  were  made  : 

(1)  Resistance  between  No.  I  wire  and  the  ground. 

(2)  Resistance  between  No.  i  and  No.  2  wire. 

The  first  gave  a  4-  b  +  c. 

The  second  gave  a  +  a1  +  b  +  b' , 

Add  together  the  ground  tests  of  No.  i  and  No.  2,  gives 
a  +  a1  +  b  +  b'—  2  c. 

By  contact  test  a  +  a'  +  b  +  b' . 

Subtract  the  latter  from  the  former,  and  divide  by  2  gives  resistance  of  pole. 

c 
The  mean  of  a  number  of  tests  gave  for  the  per  cent,  value  of :  of 


FIG.  107.    Resistance  of  Insulators, 
Poles,  and  Arms. 


&  -f  b 


the  total  insulation  : 


Maximum 22 

Minimum n 

Mean.  .  15 


134 


Telegraph ic  Circu  its. 


The  insulating  power  of  the  wet  pole  added  to  that  of  the  insulator  and 
cross-arm  was  found  to  be  as  follows  : 


\7I 


New  York  to  New  Haven.. 
New  York  to  Philadelphia., 
Mean 


15  to  22  per  cent, 
ii  to  12  per  cent. 
15  per  cent. 


A  test  from  New  York  to  Boston  between  two  wires, 
a  and  b,  placed  one  above  the  other,  as  in  Fig.  108,  on 
insulators  and  brackets  on  opposite  sides  of  the  same 
pole,  gave  the  following  mileage  insulation  : 

Wire  a  to  ground 3, 050  ohms  per  mile. 

Wire  b  to  ground 3, 700      "        "        " 


Wire  a  to  b  through  the  pole 


900 


6,750 

5,850 

900 


c  =  -  =  450  ohms  per  mile. 


FIG.  108.   Resistance  of 

Vertical  Pole. 


_  .  .  ,.        .  r 

From  this   it  appears  that  the  application  of 
ground-wires  to  the  poles  would  reduce  the  total 
insulation  about  15  per  cent.,  and  weaken  the  signals  perhaps  3  per 
cent.  ;  but,  on  the  other  hand,  it  would  eliminate  disturbing  currents 
amounting  to  about  18  per  cent,  of  the  total  strength  of  signals. 

252.  Tests  of  Resistance  of  Cross-  Arms.  —  The  following 
measurements  were  made  of  cross-arms  taken  down  from  pole-lines 
in  New  York  City.     They  show  the  insulation  resistance  per  mile  of 
40  arms  : 

All  four  surfaces  wet  with  sponge  ..................  3,  120  ohms. 

Soaked  one  day,  left  to  dry  one  day,  and  then  wet.  .  .  2,680  " 

Painted  three  years  since  ..........................  6,150  " 

Same  washed  .....................................  9,  166 

Very  dry  ...............................   11,00010330,000  " 

Newly  painted  ....................................   7,214  " 

Unpainted  for  many  years  .........................  4,300  " 

Same  after  having  been  well  washed  ................  13,657  " 

Dry  ..............................................  80,000  " 

Arms  and  pins  together  (wet)  ......................  3,686  '* 

253.  Tests  of  Glass   Insulators.  —  Measurements   made  of 
dirty  and  soot-covered  glass  and  pin  insulators,  taken  down  in  New 
York,  resulted  as  follows  : 

Dipped  in  water  once  (per  mile  of  40)  .................   23,220  ohms. 

Dipped  in  water  4  times  (per  mile  of  40)  ...............   56,400 

New  insulator  and  pins  direct  from  supply  department..  66,600      " 


Best  Method  of  Improving  Efficiency.       135 

These  figures  show  in  a  striking  manner  the  surface  deterioration 
of  glass  insulators  by  exposure  to  the  smoke  and  dirt  of  a  large  city. 
Cleaning  them  nearly  tripled  their  insulating  power.5 

254.  Importance    of    High    Working    Efficiency.— The 
importance  of  maintaining  in  telegraph  lines  as  high  a  ratio  of  insu- 
lation to  conductivity  resistance  as  possible,  is  shown  in  a  striking 
manner  by  the  figures  given  in  Table  X.     For  example,  suppose  it 
were  required  to  determine  the  effect  of  increasing  the  ratio  of  effi- 
ciency of  a  given  circuit  from  i  :  10,000,  the  basis  on  which  the  table  is 
computed,  to  i :  20,000.     This  might  be  effected,  either  by  doubling 
the  resistance  of  the  insulators,  or  by  halving  the  resistance  of  the 
line  ;  that  is,  8  megohm  insulators  might  be  used  instead  of  4,  or  wire 
of  5  ohms  per  mile  instead  of  10,  either  of  which  would  affect  the 
ratio  in  like  manner.     But  the  resistance  of  the  line,  referred  to  in 
(242),  taken  in  units  of  the  first  column  of  Table  X,  is  now  only 
1,000  instead  of  2,000,  and  the  percentage  of  received  currents  is 
therefore  raised  from  26.6  to  64.8.     On  a  line  of  250  miles,  it  would 
be  raised  from  14.7  to  52.9;  that  is,  more  than  3^  times  as  much 
current  would  be  received  at  the  end  of  the  line. 

255.  Best  Method  of  Improving  Efficiency.— A  line  of 
400  miles  of  No.  9  iron  wire  of  15  ohms  conductivity  resistance  per 
mile,  and  carried  upon  glass  insulators  giving  4.5  megohms  each  in 
very  unfavorable  weather,  with  30  poles  per  mile,  would  have  an  effi- 
ciency ratio  (242)  of  i  :  10,000,  the  same  as  that  assumed  in  Table  X. 
The  true  conductivity  of  the  line  would  be  6,000  ohms,  and  the  per- 
centage of  the  entering  current  which  would  reach  the  distant  end 
would  be  only  2.15.      If  a  copper  wire  of  5  ohms  per  mile  were  sub- 
stituted, without  changing  the  insulation,  the  percentage  of  current 
received  would   at  once    be  increased  from  2.15  to  26.6,  or   more 
than   10  times  as  much,   the  efficiency  ratio  being  now  i  :  30,000. 
The  cost  of  the  respective  wires  for  400  miles  would  be  approxi- 
mately as  follows : 

71,120  Ibs.  of  hard  copper  wire,  .20  cents $14,344 

128,000  Ibs.  of  galv.  iron-  wire,  .05  cents 6,400 

Difference  in  cost $7,944 

The  same  or  a  better  result  may  be  more  advantageously  reached 
by  improving  the  insulation.  If,  for  example,  instead  of  the  4.5 
megohm  glass  insulators,  the  German  porcelain  insulators  of  Fig. 
92,  p.  118,  were  used,  the  minimum  resistance  of  which,  according 

s  CROMWELL  F.  VARLEY  :  Report  on  Lines  of  Western  Union  Telegraph  Co. 
(Ms.),  1867. 


136 


Telegraphic  Circuits. 


to  the  test,  p.  120,  is  19  megohms,  we  may  safely  assume  that  the 
insulation  will  be  three  times  as  high  as  with  the  glass.  This  will 
give  us,  with  the  i5-ohm  wire,  an  efficiency  ratio  per  mile  of 
15  :  450,000  or  i  :  30.000,  as  before. 

The  comparative  cost  would  then  be  approximately  as  follows  : 

12,000  German  porcelain  insulators  (Fig.  92),  .25  cents $3,ooo 

12,000  Best  glass  and  bracket  (Fig.  88),  .05  cents 600 


$2,400 

It  appears,  therefore,  that  the  operative  value  of  a  long  line  in  wet 
weather  may  be  increased  as  much  by  expending  $2,400  in  improv- 
ing its  insulation,  as  by  expending  $7,944  in  improving  its  conduc- 
tivity. On  the  other  hand,  it  must  be  taken  into  consideration  that 
when  the  line  is  designed  to  be  employed  for  multiple  transmission,  a 
marked  advantage  results  from  high  conductivity,  altogether  irre- 
spective of  the  question  of  insulation  efficiency.  Several  different 
strengths  or  values  of  current,  in  this  case,  require  to  be  distin- 
guished from  each  other  by  the  selective  action  of  the  receiving 
instruments,  and  the  certainty  with  which  this  can  be  effected 
depends  largely  upon  the  maximum  volume  of  current  which  the  line 
is  capable  of  transmitting.  The  interference  arising  in  fine  weather 
from  static  induction  (314)  is  also  relatively  much  less  marked  upon 
lines  of  high  conductivity. 

256.  The  beneficial  effects  of  improving  the  insulation  on  long  cir- 
cuits are  forcibly  exhibited  in  the  following  table,  which  contains  the 
results  of  computations  made  by  Moses  G.  Farmer.6 

TABLE     XI. 

Distances  in  miles  to  which  a  stated  percentage  of  entering  current  will  reach, 
on  a  line  of  18  ohms  conductivity  resistance  per  mile,  with  insulators  of  various 
resistances. 


Per  cent,  of  en- 
tering current  re- 
ceived. 

Insulation  Resistance  (Megohms  per  Insulator)  30  Insulators 
per  mile. 

I 

4 

9 

16 

36 

100 

1000 

1600 

10% 
25 
50 
75 
90 

125 
89 
58 
36 
22 

258 
178 
116 
73 
45 

386 
267 
174 
109 
67 

5i6 
356 
232 
146 
9° 

774 
534 
348 
219 

T35 

1290 
890 

580 
365 

235 

4094 

2837 
1850 

1161 
766 

5160 
356o 
2820 
1460 
900 

6  The  Telegrapher,  v.  269. 


Best  Method  of  Improving  Line  Efficiency.     137 

These  results  seem  scarcely  credible  to  those  who  have  accus- 
tomed themselves  to  the  belief  that  the  defects  of  insulation  on  our 
existing  lines  are  unavoidable,  and  that  the  only  available  remedy  is 
the  costly  one  of  increased  conductivity.  Yet  the  correctness  of  the 
theory  is  abundantly  proved  by  the  working  of  such  a  line,  for  exam- 
ple, as  the  Atlantic  Cable  of  1866,  which  was  2,185  miles  in  length ; 
had  a  resistance  of  about  3.7  ohms  per  mile,  a  total  of  over  8,000 
ohms  ;  and  which  worked  well  with  an  c.  m.  f.  of  10  volts,  because 
of  its  high  insulation.  It  is  also  a  familiar  fact  that  any  good  line 
can  be  worked  at  full  speed  for  a  distance  of  more  than  1,000  miles 
in  cold  dry  weather,  when  the  leakage  due  to  imperfect  insulation  is 
almost  imperceptible  even  with  sensitive  measuring  instruments. 


CHAPTER    VIII. 

EQUIPMENT  OF   AMERICAN   TELEGRAPH   LINES. 

257.  Apparatus  Essential  in   Telegraphy. — It  has  been 
stated  that  the  art  of  electric  telegraphy  consists  in  the  production, 
control,  and  organization  of  electric  signals,  which  may  be  either 
visible  or  audible  (2).      The  system   of  telegraphy  now  generally 
used  in  America  under  the  name  of  the  "  Morse,"  produces  audible 
signals  at  a  distance  by  means  of  an  instrument  called  a  sounder, 
which  comprises  an  electro-magnet ;    a  vibrating  armature  ;   and  a 
key  consisting  essentially  of  a  lever  and  contact-points,  whereby  the 
transmitting  operator  is  enabled  to  interrupt  and  restore  the  circuit 
with  convenience  and  rapidity,  for  the  purpose  of  forming  the  con- 
ventional signals. 

258.  Construction  of  the  Key. — The  key  is  made  in  many 
different  forms,  not  essentially  differing  in  principle.      Its  essential 
portions  consist  of  the  lever,  the  finger-knob,  the  spring,  the  switch  or 
circuit-closer  and  the  base.     The  lever,  which  was  formerly  made  of 
cast  brass,  is  now  more  usually  punched  from   sheet  steel,  which 
renders  it  not  only  stronger  but  of  less  weight  and  more  easy  to  be 
manipulated  with  rapidity. 

A  pattern  of  key  much  used  is  shown  in  Fig.  109.  The  lever  A, 
4  or  5  inches  in  length,  slightly  curved,  is  provided  with  trunnions 
at  G,  which  turn  between  adjustable  set-screws  D  D.  The  lever  has 
a  small  vertical  reciprocating  movement  upon  its  axis,  limited  in  one 
direction  by  the  adjustable  set-screw  F,  and  in  the  other  by  a  platinum 
contact-point  c  inserted  in  a  brass  stud  C,  insulated  from  the  frame  M 
of  the  key.  The  finger-knob  or  button  B,  usually  of  non-conducting 
material,  enables  the  key  to  be  conveniently  depressed  at  pleasure 
by  the  finger  of  the  operator.  This  action  brings  a  platinum  contact- 
point  d,  inserted  in  the  under  side  of  the  lever  A,  into  contact  with 
the  one  above  mentioned  which  forms  a  part  of  the  anvil.1  One  of 

1  Platinum  is  used  for  these  and  other  contact-points  in  electrical  apparatus,  for  the 
reason  that  the  infusible  properties  of  this  metal  prevent  it  from  being  oxidized  by  the 
electric  spark,  which  tends  to  pass  between  separated  conductors  whenever  the  circuit 
is  broken.  This  spark,  in  the  case  of  the  key,  is  principally  due  to  the  inductive  eft's- 

138 


Modifications  of  the  Key. 

the  circuit-wires  P  is  clamped  to  the  brass  rod  J  by  means  of  a 
clamp-screw  L  underneath  the  table,  this  rod  being  in  metallic  con- 
nection with  the  base.  The  other  circuit-wire  is  attached  by  means 
of  another  clamp-screw  K  to  a  similar  brass  rod  I,  connected  with 
the  anvil,  and  insulated  from  the  frame.  When  the  key-lever  A  is 
depressed,  the  circuit  between  the  wires  P  and  N  is  closed,  precisely 
as  if  the  wires  themselves  had  been  brought  into  contact  with  each 
other. 

When  the  pressure  of  the  finger  is  withdrawn,    the   adjustable 
spring  E  beneath    the    lever   A,  restores    the  latter  to  its  normal 


.  109.     Bunnell's  Steel-  Lever  Key. 


position.  The  upward  pressure  of  this  spring  is  adjusted  by  means 
of  a  set-screw  H.  When  the  key  is  not  in  use,  the  main  circuit  is 
closed  by  shoving  the  pivoted  switch-lever  S  into  a  recess  formed 
between  the  lip  of  anvil  C  and  the  frame  M,  thus  establishing  an 
electrical  connection  between  the  wires  P  and  N,  notwithstanding 
the  separation  of  the  contact-points  c  and  d. 

259.  Modifications  of  the  Key.—  Of  late  years  other  forms 
of  keys  have  been  much  used,  in  which  trunnions  are  dispensed  with. 
One  of  these  is  shown  in  Fig.  no.  The  lever  is  secured  to  a  rear- 

charge  of  the  electro-magnets  in  the  circuit  ;  when  there  are  a  great  number  of  these, 
the  spark  sometimes  becomes  very  troublesome  (196).  Iridium,  another  infusible 
metal,  is  sometimes  used  instead  of  platinum. 


140      Equipment  of  ~1  nit  rican  Telegraph  Lines. 

wardly  extending  flat  steel  spring,  the  opposite  end  of  which  is  firmly 
fastened  by  screws  to  the  base.  An  adjustable  set-screw  passes 
through  a  hole  in  the  center  of  the  spring  and  its  nut  may  be  set  to 


FIG.  no.     Western  Electric  Key. 

bear  upon  its  upper  surface,  thus  enabling  its  flexibility  to  be 
regulated  as  desired.  A  second  check-nut  is  capable  of  adjustment 
to  regulate  the  stroke,  or  extent  of  vertical  vibration  of  the  key-lever. 
A  modification  which  is  applicable  to  all  keys,  consists  in  placing 
two  binding-screws,  one  of  which  is  insulated,  upon  the  top  of  the 
base  as  in  Fig.  in,  to  which  the  wire  connections  are  made,  thus 
avoiding  the  necessity  of  boring  holes  through  the  table,  which  is 
sometimes  objectionable. 


FIG.  in.     Victor  Key. 


260.  Adjustment  of  the  Key. — In  adjusting  a  key  for  work, 
the  best  result  will  usually  be  attained  by  giving  the  lever  a  small 
movement  with  a  moderate  upward  spring-pressure.  Trunnion  keys 
should  be  carefully  adjusted,  so  as  to  prevent  unnecessary  lateral 
movement  on  the  one  hand,  and  unnecessary  friction  on  the  other. 


The  Sounder. 


141 


A  trunnionless  key,  working  upon  knife-edged  bearings,  now  very 
extensively  used  and  known  as  the  "Victor,"  is  shown  in  Fig.  nr. 
By  this  device,  friction  and  weight  are  reduced  to  a  minimum,  while 
adjustment  is  rendered  more  convenient.  In  this  and  in  the  preced- 
ing pattern  of  keys,  the  electrical  contact  being  made  through 
continuous  metal,  is  more  perfect  than  is  possible  when  trunnions 
are  used. 

261.  The  Sounder. — The  essential  parts  of  this  instrument, 
shown  in  outline  in  Fig.  112,  are  an  electro-magnet  E,  usually  about 


FIG.  112.     Elevation  of  Sounder. 

the  size  and  proportion  of  .that  shown  in  Fig.  69,  page  91,  and  an 
armature  A  fixed  transversely  upon  a  brass  lever  B  about  3  inches  in 
length,  fitted  with  trunnions  at  C  and  mounted  between  transverse 
set-screws  in  the  same  manner  as  the  key.  Two  other  set-screws  D 
and  F  form  adjustable  stops,  which  limit  the  vertical  motion  of  the 
lever  in  each  direction.  When  the  circuit  is  closed  through  the 
electro-magnet,  the  armature  is  strongly  attracted,  and  is  thereby 
made  to  strike  forcibly  against  a  sounding-post  or  bridge  G  through 
which  the  vibration  is  imparted  to  the  table  upon  which  the  instru- 
ment is  secured.  When  the  magnetism  disappears,  the  lever  is 
thrown  against  the  upper  stop  F  by  the  recoil  of  an  adjustable  spring 
H.  The  operator  interprets  the  signals  by  mentally  noting  the 
difference  in  character  between  the  sounds  of  the  down-stroke  and 
the  up-stroke,  and  by  estimating  the  space  of  time  intervening 
between  them,  as  will  be  hereinafter  explained  (378).  Fig.  113  is  a 
common  pattern  of  sounder,  about  two-thirds  the  actual  size.  The 
helices  of  the  electro-magnet  are  wound  with  insulated  wire,  the 
thickness  and  convolutions  of  which  depend  upon  the  strength  of 


142      Equipment  of  American  Telegraph,  Lines. 

current  with  which  the  instrument  is  designed  to  be  used.  When 
intended  for  direct  working,  in  which  case  the  sounder  is  actuated  by 
the  current  received  over  the  line  Irom  the  distant  station,  the  helices 
are  wound  with  wire  which  may  differ  in  gauge  from  number  22  to  32 
and  even  36  (see  table,  page  94)  according  to  the  length  or  resistance 
of  the  circuit  in  which  they  are  intended  to  be  used.  Ordinarily  the 
sounder  is  operated  by  a  local  battery,  consisting  of  a  single  gravity 
cell  (Fig.  4,  page  5),  in  which  case  its  electro-magnet  is  wound  with 
number  24  wire  to  a  resistance  of  about  4  ohms. 


FIG.  113.     Sounder. 

262.  Short  Line  Instrument. — When  the  length  of  the  line 
on  which  the  sounder  is  to  be  used  does  not  exceed  40  or  50  miles, 
a  convenient  and  compact  form  of  apparatus,  consisting  of  a  sounder 
and  key  mounted  on  one  base,  with  proper  electrical  connections  as 
shown  in  Fig.  114,  and  having  its  electro-magnet  wound  to  a  resist- 
ance of  20  or  30  ohms,  may  be  employed  with  advantage. 

263.  Adjustment  of  the  Sounder. — The  adjustment  of  the 
sounder  may  be  best   effected  as  follows: — First,  loosen  the  stop 
D  until  the  armature  A  rests  directly  upon  the  poles  of  the  electro- 
magnet.    Second,  set  the  trunnion-screws  upon   which  the  lever  B 
turns,  as  tightly  as  possible  without  in  the  least  binding  the  axis. 
This  can  be  determined  by  lifting  and  letting  fall  the  lever,  having 


Pocket  Apparatus. 

previously  slackened  the  spring  H.  It  should  drop  freely  when 
released.  Third,  lay  a  piece  of  paper  between  the  poles  of  the 
magnet  and  the  armature,  and  close  the  circuit  through  the  magnet, 


FIG.  114.    Combination  Sounder  and  Key. 


so  that  the  attraction  exerted  upon  the  armature  will  clamp  ttv 
paper.  Fourth,  adjust  the  screw-stop  D,  until  the  armature  i* 
raised  just  enough,  to  permit  the  paper  to  be  drawn  out  without 
friction.  Fifth,  adjust  the  stroke  by  means  of  the  screw  F. 


FIG.  115      Pocket  Sounder  and  Key. 

Sixth,  strain  the  retracting  spring  H  until  the  character  of  the 
sounds  produced  by  the  up  and  down  strokes  of  the  lever  is  satis- 
factory. 


144      Equipment  of  American  Telegraph  Lines. 

264.  Pocket  Apparatus. — Fig.    115    represents  a  convenient, 
compact,  and  exceedingly  portable  form  of  direct-working  sounder, 
having  a  key  attached,  so  as  to  form  a  complete  apparatus  for  send- 
ing and   receiving  communications.     The  engraving    is    nearly  the 
actual  size  of  the  instrument,  which,  together  with  its  case,  weighs 
but  a  few  ounces,  and  can  be  readily  carried  in  the  coat-pocket. 

265.  Box  Sounder. — Fig.  116  shows  still  another  combined  key 
and  sounder,  in  which  the  electro-magnet  is  of  standard  dimensions, 
and    is   enclosed    within    a  wooden    box,    the    resonance    of  which 
materially    increases  the   volume    of  sound    made    by    the    strokes 
of    armature-lever.     This    apparatus,    being    complete    in    itself,    is 
often  found  useful  in  the  railway  telegraph  service,  for  establishing 


KIG.  116.     Combination  Box  Sounder  and  Key. 


temporary  communication  at  any  point    along   the  line  in  case  of 
accident. 

266.  Working  by  Relay  and  Local  Circuit. — When   the 
line  is  of  considerable  length  and  corresponding  resistance  (118),  or 
its  insulation  is  defective,  as  is  usually  the   case  in  practice  (232), 
the  main  line  current  may  be  too  feeble  or    too  variable  to  satis- 
factorily operate  the  receiving  instrument.      This  inconvenience  is 
avoided  by  making   use  of  an    intermediate    receiving   instrument 
called    the    relay,   which    is   included    in    the     main    circuit.     Its 
armature-lever   has  only  to  perform   the    function  of  opening   and 
closing  the  circuit  of  a  local   battery  at    the  receiving  station,  by 
which  means  the  sounder  can  be  made  to  produce  any  required  vol- 
ume of  sound. 

267.  Construction  of  the  Relay.— The  relay  consists  of  an 
electro-magnet,  having  its  armature  delicately  poised,  so  as  to  be 
free  and  capable  of  being  acted  upon  by  minimum  magnetic  attrac- 
tion.     Fig.  117  represents  a  design  which  is  largely  used. 

Fig.  118  represents  the  working  parts  of  a  relay  in  outline.     The 
electro-magnet  M  has  its  soft  iron  cores,  usually  2   in.   long  and 


Construction  of  the  Relay. 


H5 


\\  in.  diameter,  sc^-wrd  into  a  yoke  Y,  2  in.  long  and  }  in.  in  thick- 
ness. The  standard  resistance  of  the  coils  is  about  150  ohms,  and 
the  average  number  of  convolutions  of  wire  in  the  coils  8,500.  The 


FIG.  117.     Western  Union  Relay. 

usual  magnetizing  force  is  about  200  ampere-turns  (176).  The 
front  ends  of  the  magnet  are  supported  in  a  vertical  metallic  frame 
F,  the  foot  of  which  is  firmly  secured  to  a  hard-wood  base,  by  screws 


r 


FIG.  1 18.     Elevation  of  Relay. 

from  beneath.  Two  circular  openings  are  formed  in  this  frame, 
large  enough  to  permit  the  helices  to  pass  freely  through  without  be- 
ing fastened  in  any  way.  The  yoke  end  of  the  magnet  is  supported  at 


146      Equipment  of  American  Telegraph  Lines. 

S  by  a  right  and  left  screw,  or  a  straight  screw  with  two  check-nuts 
passing  through  a  brass  pillar  fixed  upon  the  base.  This  device  is 
capable  of  imparting  to  the  electro-magnet  M  a  limited  horizontal 
advance  or  retrograde  movement.  The  armature  A  in  front  of  the 
poles  is  fixed  transversely  to  the  upright  lever  B,  the  lower  end  of 
which  is  mounted  upon  a  steel  arbor  turning  between  two  adjustable 
set-screws,  mounted  upon  standards  H  projecting  from  the  lower  part 
of  the  frame  F.  The  armature-lever  and  armature  are  permitted  a 
limited  movement  to-and-fro  upon  the  axis,  responsive  in  one  direc- 
tion to  the  attraction  of  the  electro-magnet,  and  in  the  other  the 
retractile  force  of  the  spiral  spring  T.  This  motion  is  limited  in  one 
direction  by  the  adjustable  screw-stop  C,  and  in  the  other  by  a  fixed 
stop  of  non-conducting  material  placed  within  the  slotted  projection 
D,  through  which  the  lever  B  passes  freely,  not  touching  anything 
but  the  stops.  The  spring  T  is  attached  at  one  end  to  the  lever  B 
by  a  hook,  and  at  the  other  end  to  a  thread  which  winds  upon  a 
spindle  V  provided  with  a  milled  head.  (See  Fig.  117.)  This 
spindle  is  supported  in  a  socket  upon  the  end  of  a  horizontal  brass 
rod,  which  slides  through  a  pillar  and  may  be  fastened  in  any 
required  position  by  a  check-screw.  The  object  of  this  device  is  to 
enable  the  tension  of  the  spring  T  to  be  adjusted  through  a  some- 
what wide  range,  the  necessity  for  which  will  be  hereinafter  ex- 
plained. 

The  electrical  connections  of  the  relay  are  as  follows : — Upon  the 
base  are  four  binding-screws  for  the  attachment  of  wires.  Only  three 
of  these  are  visible  in  Fig.  117,  the  other  being  concealed  by  the 
electro-magnet  M.  The  insulated  copper  wires  projecting  from  the 
helices  of  the  electro-magnet  are  seen  to  pass  down  through  the 
wooden  base,  underneath  which  they  are  connected  to  the  two 
right-hand  binding-posts,  so  that  current  entering  at  one  binding- 
post,  after  traversing  both  helices  of  the  electro-magnet,  returns  to 
the  other  and  passes  on. 

It  has  been  explained  that  the  function  of  the  relay  is  simply  to 
break  and  close  the  independent  local  circuit  in  which  the  sounder 
is  included,  whenever  the  main  circuit  is  broken  and  closed,  or  in 
other  words,  to  repeat  the  signals  of  the  main  circuit  into  the  local 
circuit.  To  this  end  the  armature-lever  A  is  carefully  insulated 
from  the  frame  F  by  a  non-conducting  bushing  interposed  between 
the  lever  and  the  axis  upon  which  it  turns.  A  wire  leads  under- 
neath the  base  from  one  binding-screw  to  the  support  of  the  arma- 
ture. Another  thin  copper  wire  W,  coiled  into  a  spiral,  connects 
the  armature-lever  with  its  support,  being  attached  to  the  former  by 


Adjustments  of  the  Relay.  147 

a  small  screw  seen  in  the  figure  just  above  the  axis.  When  the 
armature  is  attracted  by  the  electro-magnet,  a  platinum  contact- 
point  near  the  top  of  the  lever  B  (Fig.  118)  is  brought  in  contact 
with  a  corresponding  platinum  point  which  forms  the  tip  of  the 
adjustable  screw-stop  C.  The  stop  C  is  in  electrical  connection 
with  the  brass  frame  F,  and  this  is  in  turn  connected  with  the  ex- 
treme left-hand  terminal  binding-post  by  a  wire  under  the  base. 
Hence  it  necessarily  follows  that  whenever  the  two  platinum  points 
are  brought  in  contact  by  the  advance  movement  of  the  armature- 
lever  in  response  to  the  attraction  of  the  electro-magnet,  a  connec- 
tion will  be  formed  between  the  two  terminals  completing  the  local 
circuit  through  the  sounder. 

268.  Adjustments  of  the  Relay.— The  adjustments  of  the 
relay  are  three  in  number  :  first,  the  stroke,  or  extent  of  the  to-and-fro 
movement  of  the  armature ;    second,  the  antagonistic  action  of  the 
retracting  spring;  and  third,  the  distance  between  the  armature  and 
the  poles  of  the  magnet. 

The  first-mentioned  adjustment  is  effected  by  the  front  screw-stop 
C,  which  is  movable,  the  rear  stop  being  fixed.  The  maximum  sepa- 
ration between  the  platinum  contacts  ought  never  to  exceed  ^  of  an 
inch,  and  in  case  the  actuating  current  is  weak,  it  should  be  made  as 
much  less  than  this  as  possible.  Under  ordinary  conditions  this 
adjustment,  once  properly  made,  seldom  requires  alteration.  The 
second  adjustment  particularly  requires  judgment  and  skill  on  the 
part  of  the  operator.  When  the  attraction  of  the  electro-magnet  is 
very  strong,  as  is  usually  the  case  in  wet  weather  (242),  the  armature 
will  not  fall  off  promptly,  and  hence  the  tension  of  the  spring  must 
be  increased  by  turning  the  milled  head,  thus  winding  the  thread  and 
straining  the  spring.  The  spring  T  must  never  be  wound  around  the 
spindle  V.  When  the  thread  has  all  been  taken  up,  the  spindle 
must  be  removed  to  a  greater  distance  from  the  armature,  by  loosen- 
ing the  check-screw  and  sliding  the  rod  upon  which  it  is  mounted 
through  the  post  to  a  sufficient  distance  and  then  clamping  it  again. 
In  extreme  cases  the  tension  cannot  be  sufficiently  increased  by  this 
means,  and  it  then  becomes  necessary  to  resort  to  the  third  adjust- 
ment, which  consists  in  withdrawing  the  magnet  by  the  screws,  so  as 
to  increase  the  distance  between  the  poles  of  the  electro-magnet  and 
the  armature. 

269.  The  Register. — This  apparatus  for  recording  the  signals, 
was  originally  regarded  as  an  essential  part  of  the  Morse  system. 
It  is  now  but  little  used  except  at  small  stations  and  on  railway  lines. 
It  consists   essentially  of  a  pair  of  grooved   rollers   moved   at   a 


148      Equipment  of  American   Telegraph  Lines 

uniform  rate  by  a  system  of  controlled  clock-work  driven  by  a  weight 
or  spring.  A  long  narrow  strip  or  ribbon  of  paper,  taken  from  a  roll, 
passes  between  adjustable  guides,  and  thence  between  the  grooved 
rollers,  the  motion  of  which  draws  it  along  from  right  to  left  at  a 
uniform  rate.  An  electro-magnet  is  provided  with  a  lever  similar  to 
that  of  the  sounder  (261),  and  armed  at  the  extremity  with  a  style  or 
point  of  hard  steel,  which  works  in  a  groove  rn  the  upper  roller.  As 
the  strip  of  paper  passes  between  the  rollers,  a  raised  line  is 
embossed  upon  the  upper  surface  of  the  paper  whenever  the  mark- 
ing point  is  forced  into  the  groove  by  the  attraction  of  electro-mag- 
net exerted  upon  the  armature  at  its  opposite  end  of  the  lever.  A 
retracting  spring  is  provided  with  adjustments  similar  to  those 
described  in  connection  with  the  sounder.  The  paper-guide  is 
capable  of  lateral  adjustment,  so  that  the  same  strip  of  paper  may, 
if  desired,  be  used  several  times,  each  successive  line  of  characters 
lying  parallel  to,  and  in  front  of  the  preceding  one. 


FIG.  119.    European  Pattern  Register. 

270.  Fig.  119  shows  one  of  the  most  modern  forms  of  the  regis- 
ter, in  which  the  clock-work  is  propelled  by  a  coiled  spring,  instead 
of  by  a  weight,  as  in  the  instruments  formerly  made.  The  ma- 


Adjustments  of  the  Register. 


149 


chinery  is  entirely  enclosed  in  a  brass  case  with  plate-glass  panels,  so 
as  to  exclude  dust.  The  end  of  the  strip  of  paper  is  inserted 
through  the  guide  and  between  the  rollers  while  the  clock-work  of  the 
register  is  in  motion.  The  rate  of  speed  at  which  the  paper  moves 
may  be  varied,  within  certain  limits,  by  means  of  a  governor  acting 


FIG.  120.     Combination  Victor  Key,  Relay,  and  European  Register. 

upon  the  retarding  or  controllling  device  of  the  clock-work.  The 
register,  relay,  and  key,  are  sometimes  combined  upon  a  single  base 
with  their  necessary  connections,  as  in  Fig.  120. 

271.  Adjustments  of  the  Register. — The  armature  must  be 
so  adjusted  as  not  to  come  quite  in  contact  with  the  poles  of  the 
electro-magnet  (262).  After  the  set-screw  which  limits  the  move- 
ments of  the  armature  toward  the  electro-magnet  has  been  properly 
adjusted,  the  armature  should  be  held  down,  either  by  closing  the 
local  circuit  through  the  electro-magnet  or  by  the  finger ;  the  register 
is  then  started,  allowing  the  paper  to  run,  and  the  marking-point 
adjusted,  by  turning  its  milled  head  until  a  continuous  uniform  line 
is  produced  upon  the  upper  surface  of  the  paper,  by  the  action  of  the 
style  between  the  groove  and  the  roller.  The  embossed  line  should 
not  be  made  any  deeper  than  to  enable  it  to  be  distinctly  seen  when 


150      Equipment  of  American  Telegraph  Lines. 

placed  in  a  transverse  light  in  front  of  a  window.  The  final  adjust- 
ment is  that  of  the  set-screw  which  limits  the  movement  of  the 
armature  away  from  the  electro-magnet,  which  should  be  so  fixed 
that  the  marking-point  will  just  clear  the  paper  when  released  by  the 
breaking  of  the  circuit. 

272.  Causes  of  Defective  Marking. — Imperfect  marks  will 
result  if  the  style  does  not  work  accurately  in  the  groove  of  the 
upper  roller.     This  defect  is  usually  due  to  the  working  loose  of  the 
screws  which  form  the  transverse  bearings  of  the  axis  of  the  marking 
lever,  so  as  to  permit  too  much  lateral  play,  and  may  obviously  be 
remedied  by  proper  adjustment  (260).     When  such  adjustment  has 
been  effected  it  should  be  let  alone.     The  unnecessary  alteration  of 
the  adjustment  of  the   pen-lever   is  frequently  the  cause  of  much 
trouble  to  inexperienced  operators. 

273.  Ink- Writing  Register. — A  form  of  register  now  much 
used  is  shown  in  Fig.  121,  in  which  the  characters  are  marked  upon 
the    upper    surface    of    a    narrow 

strip  of  paper  by  means  of  a  small 
sharp  -  edged  jockey  -  wheel,  driven 
by  the  clock-work  and  supplied  with 
ink  by  means  of  a  felt  roller  sat- 
urated with  thick,  oily  ink,  which 
revolves  in  contact  with  it,  being 


FIG.  121.     Ink- writing  Register. 


held  thereto  by  a  spring.  A  knife-edge  on  the  end  of  the  armature- 
lever,  lifts  the  slack  of  the  paper  into  forcible  contact  with  the 
tinder  edge  of  the  revolving  inked  jockey-wheel,  whenever  the  arma- 


Circiiits  of  the  American  System.  151 

ture  is  attracted,  and   thus    the  characters  are  plainly  recorded  in 
black  ink. 

274.  Circuits  of  the  American  System.— Telegraphic  cir- 
cuits in  the  United  States  and  Canada  are  almost  universally  arranged 
upon  the  modification  of  the  closed-circuit  system,  shown  in  Fig.  83, 
page  1 08.     If  an  operator  at  any  station  desires  to  transmit  a  com- 
munication, he  first  opens  the  switch  of  his  key  and  interrupts  the 
flow  of  current  throughout  the  line.     This  causes  the  armatures  of  all 
the  relays  in  the  circuit  to  fall  off.     He  then  proceeds  to  manipulate 
his   key,   by  closing  and   breaking   the  circuit  at  accurately  timed 
intervals,  so  as  to  form  the  conventional  characters  of  the  telegraphic 
code  in  the  order  required  to  spell  out  his  communication.     During 
this  operation,  the  armatures  both  of  his  own  and  of  all  the  other 
relays  in  the  circuit,  as  well  as  those  of  the  registers  or  sounders  con- 
nected therewith,  will  respond  instantaneously  to  every  movement  of 
the  key,  and  consequently  the  communication  may  be  copied  from  the 
sounder  or  register  by  an  operator  either  at  any  one  station,  or  if 
required,    at    all    the    stations    simultaneously.       As    the    receiving 
instrument  of  the  sending  operator  normally  responds  to  every  move- 
ment of  his  key,  it  is  evident  that  the  receiving   operator   at   any 
station  may  interrupt  him  at  any  time,   by   opening  his   own   key, 
and  thus  breaking  the  circuit  in  another  place.     The  sending  oper- 
ator instantly  perceives  such  an  interruption,  by  reason  of  the  failure 
of  his  relay  and  sounder  to  respond  to  the  movements  of  his  own 
key. 

275.  Arrangement  of  Apparatus  at  a  Way-Station.— 
The  simplest  complete  combination  of  apparatus  is  that  found  at  an 
intermediate  or  way-station  having  but  a  single  main  wire.     It  com- 
prises one  set  of  instruments,  viz :  a  key,  sounder  or  register,  relay, 
local  battery,  switch,  lightning  arrester,  and  the  wires  connecting  the 
different  parts  of  the  apparatus.      The  manner  in  which  these  are 
usually  arranged  and  connected  with  each  other,  and  with  the  line, 
will  be  understood  by  reference  to  Fig.  122,  which  represents  a  com- 
plete way-station. 

The  sounder,  relay  and  key  may  be  conveniently  placed  upon  a 
table  about  two  feet  by  three  in  size.  The  sounder,  or  its  equivalent 
the  register,  is  best  placed  in  the  middle  of  the  length  of  the  table, 
having  the  key  on  the  right  and  the  relay  on  the  left.  The  knob  of 
the  key  should  be  about  12  in.  from  the  front  edge  of  the  table. 
The  switchboard  is  most  usually  placed  in  an  upright  position  upon 
the  wall  above  the  table,  or  in  any  convenient  position.  The  switch- 
board is  not  absolutely  necessary,  but  it  is  a  very  convenient  device 


152     Equipment  of  American  Telegraph  Lines. 


for  making  the  necessary  changes  in  the  connections  of  the  wires. 
In  the  form  most  commonly  employed  (see  Fig.  131)  a  device  is  used 
similar  to  that  described  in  connection  with  the  rheostat  (Fig.  43,  p. 


TO  NEW  YORK 


TO  PHILADELPHIA 


L1 


SWITCHBOARD 


r               i                   ^ 

— 

\ 

i 

x,    ,'"  I 

.1 

/ 

A       A 

1    ' 

0-- 

/                     i  \-J\ 

RELAY 

SOUNDER 

fr^ 

O~ 

TABLE 


KEY 


LOCAL  BATTERY 


FIG.  122.    Diagram  of  Way-Station. 


GROUND 


51),  a  number  of  metallic  pegs  with  insulating  handles  adapted  to  be- 
inserted  between  the  edges  of  thick  plates  of  brass,  between  which 
they  form  an  electrical  connection. 

276.  Connections  of  Apparatus  of  Way-Station. — The 
way-station  in  the  diagram  Fig.  122,  may  represent  for  instance, 
Trenton,  N.  J.;  L  being  the  line-wire  from  New  York  to  Trenton, 
and  L1,  the  line-wire  from  Trenton  to  Philadelphia.  The  line-wires 
are  extended  into  the  station  building  by  leading-in  wires  properly 
insulated,  which  are  connected  with  the  binding  screws  i  and  2  of" 


Manipulation  of  tkc  Switchboard. 


153 


the  switch.  These  binding  screws  aie  mounted  upon  vertical  me- 
tallic bars  secured  to  the  wooden  back-board  vsee  Fig.  131).  Of 
the  instrument  wires  il  leads  from  the  binding  screw  4  of  the  switch 
to  one  of  the  terminal  screws  of  the  key.  From  the  other  terminal 
screw  of  the  key,  the  wire  i  extends  to  the  first  right-hand  main 
terminal  of  the  relay;  the  other  instrument  wire  /a  unites  the  bind- 
ing screw  5  of  the  switch  to  the  second  right-hand  terminal  of  the 
relay;  a  wire  g  leads  from  the  binding  screw  3  of  the  switch  to  the 
ground  (210).  The  wires  of  the  local  or  office  circuit  are  run  as 
follows  : — From  the  local  battery,  the  wire  e  runs  to  the  first  left-hand 
(local)  terminal  of  the  relay;  the  wire/runs  from  the  second  left- 
hand  (local)  terminal  of  the  relay  to  one  terminal  of  the  sounder  or 
register ;  and  finally  the  wire  h  runs  from  the  remaining  terminal  of 
the  sounder  or  register  to  the  other  pole  of  the  local  battery.  It 
is  quite  immaterial  which  pole  of  the  battery  is  connected  to  the 
relay  and  which  to  the  sounder. 

277.  Manipulation  of  the  Switchboard. — The  various 
changes  which  may  be  made  upon  the  one-line  switch  for  different 
purposes  are  as  follows : 

(i.)  To  cut  out  the  Apparatus. — Insert  pegs  connecting  i  and  2 
with  6,  as  in  Fig.  123.  The  main-line  current  now  passes  from  the 
4-  pole  of  the  main  battery  at  New  York  through  the  instrument  at 
that  station,  and  thence  over  the  line  L  to  i,  and  through  6  to  2, 
thence  over  the  line  L1,  and  through  the  apparatus  at  Philadelphia  to 
the  —  pole  of  the  main  battery  at  that  place,  and  thence  to  the 
ground.  The  -  -  pole  of  the  New  York  battery  is  also  connected 
with  the  ground,  and  therefore  the  circuit  is  complete.  When  thus 


FIG.  123. 


FIG.  124. 


FIG.  125. 


FIG.  126. 


FIG.  127. 


arranged,  it  will  be  seen  that  the  ground  wire  g,  and  also  the  instru- 
ment wires  i1  and  /3  at  the  way-station,  are  entirely  disconnected 
from  the  main  line. 

This  is  the  manner  in  which  the  pegs  of  the  switch  should  always 
be  arranged  when  the  operator  is  absent  from  the  office  or  during  the 
prevalence  of  a  thunder-storm. 

In  some  of  the   switches  in  use,  the  cut-out  bar  6   is   omitted 
When  this  is  the  case,  the  holes  on  bar  5  should  both  be  pegged, 


154      Equipment  of  American    Telegraph  Lines. 

and  the  others  left  open  (Fig.  124).  The  key  (Fig.  122)  should 
also  be  opened,  which  serves  to  disconnect  the  wire  i1  ;  i*  being 
open  at  the  switch.  This  prevents  lightning  from  injuring  the 
instruments.  In  thus  cutting-out  by  means  of  one  of  the  instrument 
wires,  the  one  which  runs  to  the  key  should  always  be  made  use  of, 
not  the  one  going  to  the  relay. 

(2.)  To  cut  in  the  Apparatus. — Insert  pegs  in  1-5 'and  2-4  (Fig. 
125)  or  else  in  1-4  and  2-5  (it  is  immaterial  which,  though  the 
former  is  most  usual),  and  remove  the  pegs  from  1-6  and  2-6,  taking 
care  that  the  remainder  of  the  holes  are  also  open.  It  is  better  to 
peg  holes  1-5  and  2-4  before  taking  out  1-6  and  2-6,  which  can  read- 
ily be  done  if  four  pegs  are  provided,  as  then  the  circuit  of  the  main 
line  need  not  be  interrupted  even  for  an  instant.  Care  should 
always  be  taken  before  "cutting  in  "  the  instruments  to  see  that  the 
key-switch  is  closed. 

If  Nos.  1-5  and  2-5  are  used  for  cutting  out,  close  the  key,  insert 
peg  at  1-4,  and  afterwards  remove  peg  from  1-5. 

278.  Testing  for  Disconnection.— In  case  the  line  is  broken, 
or  the  circuit  is  open,  as  it  is  termed,  it  becomes  necessary  for  the 
way-station  to  test  the  circuit.  This  is  done  by  grounding  the  line. 
Suppose  the  line  disconnected  at  some  unknown  point.  Trenton 
already  has  pegs  in  the  holes  1-5,  and  2-4  (Fig.  125),  as  in  the  ordi- 
nary manner  of  working,  but  of  course  perceives  no  current.  A 
spare  peg  is  placed  in  1-6  (Fig.  126),  the  effect  of  which  is  to  connect 
the  end  of  the  New  York  line  L  with  the  earth  wire  g.  This  com- 
pletes the  circuit  of  the  New  York  battery,  but  produces  no  effect  on 
the  Trenton  instrument,  as  the  current  does  not  pass  through  it. 
The  peg  is  then  transferred  from  1-6  to  2-6  (Fig.  127).  The  cir- 
cuit of  the  New  York  battery  is  again  completed  as  before,  except 
that  it  now  includes  the  Trenton  instrument,  its  course  being  from  the 
line  wire  L  through  the  instruments  as  usual,  and  through  the  peg  2-6 
to  the  wire  g,  and  finally  to  the  ground.  Trenton  now  becomes  a 
terminal  station,  working  with  New  York  by  means  of  the  battery 
at  the  latter  place. 

This  result  demonstrates  to  the  operator  at  Trenton  that  the  dis- 
connection is  between  that  place  and  Philadelphia.  If,  on  the  con- 
trary, the  circuit  had  been  completed  through  the  relay  when  the  peg 
was  inserted  in  6,  it  would  have  shown  the  break  to  have  been  in  the 
opposite  direction. 

It  sometimes  occurs  that  the  circuit  cannot  be  completed  on  either 
side,  and  the  line  appears  therefore  to  be  interrupted  in  both  direc- 
tions. In  that  case  the  trouble  is  in  all  probability  within  the  limits 


The    Wedge  Cut-Out. 


155 


FIG.  128. 


Switch  Wedge  or 
Plug. 


of  the  way-station  itself,  usually  in  the  instrument  connections,  which 
should  be  carefully  inspected. 

279.  Reporting  Result  of  Test. — If  the  operator  at  a  way- 
station  finds  by  the  above  test  that  the  line 

is  interrupted  in  a  particular  direction,  it  is 
his  duty  to  report  the  fact  at  once  to  the 
terminal  station  in  the  opposite  direction, 
from  which  he  should  receive  instructions 
in  regard  to  his  proper  method  of  pro- 
cedure, so  that  the  uninjured  portion  of 
the  line  may  be  operated  until  the  difficulty 
is  removed. 

280.  The   Wedge    Cut-Out.— This 
device  is  often  used  at  way-stations  instead 
of  the  switch  last  described.      It  is  termed  a 

plug,  or  more  prop- 
erly a  wedge  cut-out. 
The  i  n  s  tr  u  m  e  n  t 
wires,  z1  and  i2  of 
Fig.  122,  are  con- 
nected to  the  opposite  sides  of  a  wedge, 
as  it  is  technically  termed,  which  is  shown, 
full  size,  in  Fig.  128.  It  consist's  of  two* 
brass  plates  insulated  from  each  other  by  a 
thin  plate  of  hard  rubber,  and  provided  with 
a  handle  of  the  same  material.  The  ends 
of  the  line-wire  are  connected  with  the  two 
binding  screws  at  the  top  of  the  baseboard 
(Fig.  129).  The  right-hand  binding  screw 
is  connected,  by  a  wire  under  the  baseboard, 
with  an  elastic  brass  strip.  The  upper  end 
of  this  strip  is  rigidly  attached  to  the  board, 
while  the  lower  end  is  armed  with  a  brass 
pin,  which,  by  the  elasticity  of  the  strip,  is 
pressed  firmly  against  a  second  pin,  also 
screwed  to  the  board.  The  stationary  pin 
is  attached  by  means  of  a  wire  to  the  other 
binding  screw,  and  is  thus  placed  in  con- 
nection with  the  line-wire.  This  device  is 
termed  the  spring-jack.  When  the  wedge, 
carrying  the  flexible  instrument  wires,  is  inserted  between  the  two 
pins,  it  separates  them,  thereby  breaking  the  circuit  of  the  main 


;.  129 


Spring-Jack  and 
Wedge. 


156      Equipment  oj  American  Telegraph  Lines. 

line,  but  simultaneously  opening  a  new  path  for  the  current  through 
the  two  parts  of  the  wedge  and  the  instruments.  Thus  the  latter 
may  be  inserted  into  or  withdrawn  without  interrupting  the  main 
circuit,  by  a  single  instantaneous  movement.  For  many  places 
this  is  an  exceedingly  simple  and  effective  arrangement.  It  is  some- 
times used  for  large  stations,  in  combination  with  the  peg-switch, 
as  will  be  hereafter  shown  (286).  The  wedge  cut-out  is  usually  pro- 
vided with  a  lightning  arrester  and  ground-wire  connection,  ar- 
ranged with  pegs,  as  in  Fip".  ^29,  in  much  the  same  manner  as  the 
switch  in  Fig.  122. 

281.  Multiple-Wire  Switchboards. — It  very  often  happens 
that  different  lines  traversing  the  country  in  the  same  or  in  different 
directions  pass  through  the  same  way-station.  The  necessities  of  the 
service  sometimes  require  that  there  should  be  apparatus  provided 
for  each  line,  but  more  frequently  a  smaller  number  of  instruments  is 
sufficient,  provided  means  are  furnished  by  which  any  one  of  them 
can  be  inserted  into  the  circuit  of  any  line  at  pleasure. 


--.  .. 


FIG.  130.     Multiple  Spring-Jack. 

282.  Multiple  Spring- Jack.— The  simplest  way  of  providing 
for  this  is  to  make  use  of  a  number  of  spring-jacks  (Fig.  130)  cor- 
responding to  the  number  of  line  wires,  and  placed  side  by  side  upon 
the  same  baseboard.     The  wires  for  each  separate  set  of  instruments 
terminate  in  a  wedge,  and  by  this  means  any  instrument  may  be 
placed   in   connection   with   any  required   line-wire   at  a  moment's 
notice,  simply  by  inserting  its  wedge  into  the  corresponding  spring, 
jack. 

283.  Universal    Switchboard. —The    arrangement    last   de- 
scribed makes  no  provision  for  interchanging  the  line-wires  among 
themselves — a    proceeding  which  is   necessary,   for  instance,   when 


Manipulation  of  the  Universal  Siuitchboard.     157 


two  or  more  lines  running  in  the  same  general  direction  are  each  in- 
terrupted, but  at  different  points.  By  connecting  the  uninjured  por- 
tions of  different  lines  with  each  other,  it  is  often  possible  to  "patch 
up"  one  or  more  complete  circuits  for  the  transaction  of  business. 
The  wirt-s  are  interchanged  or  cross-connected,  as  it  is  termed,  at  the 
different  way-stations,  in  accordance  with  instructions  given  by  the 
official  in  charge  of  the  circuits  at  the  terminal  station.  In  order 
to  conveniently  ac- 


complish 
different 


this, 
wires 


the 
are 


Ground 


brought  into  a  switch- 
board of  sufficient 
capacity  at  each  of 
the  principal  way- 
stations,  and  the  nec- 
essary changes  are 
made  upon  this  with- 
out any  interference 
with  the  lines  them- 
selves. 

There  are  many 
varieties  of  universal 
switchboards,  but  all 
are  constructed  upon 
the  same  principle. 
This  will  be  under- 
stood by  reference  to 
Fig.  131,  which  rep- 
resents a  switch  designed  for  a  way-station  having  two  line-wires, 
lE  iW,  and  2E  2\V,  and  two  instruments  A  and  B. 

284.  Manipulation  of  the  Universal  Switchboard. — The 
various  changes,  other  than  those  which  have  been  explained  in  con- 
nection with  the  single-wire  switch  (277),  are  made  as  follows: 

(i.)  Both  lines  connected  straight,  with  both  instruments  in. — Insert 
pegs  as  in  Fig.  132,  leaving  the  remaining  holes  open. 

(2.)  Lines  cross-connected  or  interchanged. — In  this  case,  it  is  re- 
quired to  connect  No.  i  wire  west  with  No.  2  wire  east,  and  No.  i 
east  with  No.  2  west.  Insert  pegs  as  in  Fig.  133,  leaving  the  other 
holes  open.  Both  instruments  A  and  B  are  now  included  in  the 
circuit.  To  leave  instrument  A  out  of  the  circuit,  change  the  pegs 
to  the  position  shown  in  Fig.  134.  Instrument  B  is  cut  out  by 
placing  the  pegs  as  shown  in  Fig.  135.  In  Fig.  136,  the  wires  are 


•MHHHK--       ..... 

Fig.  131.     Two  line  Universal  Switch. 


158     Equipment  of  American  Telegraph  Lines. 

interchanged  and  both  instruments  cut  out,  a  proceeding  which  is 
sometimes  necessary  when  a  test  is  to  be  made. 


E  W   E  W 

O  O  O 


G    O 


EWE 

O  O  O  O 


G    O 


'to 


E 
f 

V 

)  r 

/    E 

)  r 

.  w 

)  r 

0 

£ 

E  W   E  W 

O  O  O 


G    O 


FIG.  132. 


FIG.  133. 


FIG.  134. 


FIG.  135. 


(3.)  Lines  grounded  or  put  to  earth. — This  may  be  done  on  either 
No.  i  or  No.  2  wire,  east  or  west,  by  inserting  pegs  along  the 
ground  wire  bar  G,  as  required,  as  in  the  single-wire  switch  (277). 

(4.)  Lines  looped. — It  is  sometimes  required  to  loop  two  wires,  as 
it  is  termed,  for  making  tests  or  other  purposes.  To  loop  i  and  2 
east,  with  instrument  A  in  circuit,  insert  pegs  as  in  Fig.  137  ;  with- 
out instrument  A,  insert  pegs  as  in  Fig.  138.  Numbers  i  and  2 
east  may  be  looped  in  a  corresponding  manner. 


f 
1 

-.   V 
3  C 

Y 

^   ( 

E   V 

l  r 

i? 

C, 

E  W    E 

o  o  o  o 


0 

: 

E  W    E  W 

O  O  O  O 


u  — 

ir\..\ 

In 

(U  — 

0 

FIG.  136. 


FIG.  137. 


FIG.  138. 


The  foregoing  explanation  will  sufficiently  illustrate  the  principle 
upon  which  the  switch  is  manipulated.  Switches  are  made  to  ac- 
commodate any  number  of  wires,  from  i  to  50  or  more. 

285.  Arrangement  of  the  Apparatus  at  the  Terminal 
Station. — The  simplest  possible  arrangement  at  a  terminal  station 
is  similar  to  that  shown  in  Fig.  122,  but  it  is  rare  that  such  a  station 
does  not  contain  more  than  one  line-wire.     More  than  one  line  en- 
tering a  terminal  station  renders  it  desirable  to  employ  a  switch  sim- 
ilar in  construction  to  Fig.  131,  but  with  its  connections  differently 
arranged,  for  at  a  terminal  station,  provision  must  be  made  for  con- 
necting and  disconnecting  the  main  batteries  as  well   as  the  instru- 
ments. 

286.  Terminal  Switchboards.— Fig.  139  represents  a  switch- 
board in  a  large  American  terminal  station.     In  this  switchboard 


Terminal  Switchboards. 


159 


both  the  peg-switch  and  the  wedge  cut-out  are  employed.  In  the 
largest  class  of  terminal  stations  the  switchboard  is  divided  into  a 
number  of  sections,  each  section  accommodating  a  certain  portion  of 
the  lines  entering  the  office.  The  wires  are  usually  distributed  ac- 


cording to  the  geographical  location  of  the  region  with  which  they 
connect.  The  lines  running  eastward,  for  example,  are  placed  in 
one  section  of  the  switch,  and  those  running  northward  in  another, 
while  still  another  section  accommodates  the  local  lines,  etc.,  etc. 


160      Equipment  of  American  Telegraph  Lines. 

The  switchboard  represented  in  the  figure  is  provided  with  50 
vertical  bars,  to  the  lower  ends  of  which  the  line-wires  are  connected. 
Between  each  pair  of  upright  bars  is  placed  a  row  of  metallic  disks, 
to  which  the  battery  terminals  are  connected.  All  the  disks  in  each 
separate  horizontal  row  are  electrically  united  at  the  back  by  hori- 
zontal copper  wires,  the  extreme  left-hand  disk  having  a  distinguish- 
ing number  opposite  it.  The  vertical  bars  are  connected  at  pleasure 
with  the  horizontal  disks  at  any  required  point  by  the  insertion  of  a 
peg  at  the  point  of  intersection.  Immediately  underneath  the  lower 
end  of  the  vertical  bars  are  placed  a  corresponding  number  of  spring- 
jacks.  Each  main  wire  entering  the  switch  passes  first  through  one 
of  the  spring-jacks,  and  thence  to  the  corresponding  bar.  Each 
spring-jack  bears  an  ivory  plate,  upon  which  may  be  engraved  the 
designating  number  of  the  circuit  to  which  it  is  attached. 

The  baseboard  of  the  switch  is  of  mahogany,  cut  in  strips  ,2  in. 
wide  by  i  in.  thick,  separated  by  a  space  of  -J  in.,  to  prevent  injury 
to  the  brass-work  by  shrinkage.  Each  strip  of  mahogany  supports 
two  vertical  bars  and  one  row  of  disks.  The  spring-jacks  are  held 
in  position  by  stout  spiral  wire  springs  attached  to  the  back  of  the 
switch.  One  row  of  horizontal  disks  is  connected  directly  with  the 
earth.  The  lightning  arresters  are  not  combined  with  the  switch,  as 
in  the  smaller  stations,  but  are  placed  at  the  point  where  the  wires 
first  enter  the  building.  The  instruments  seen  upon  the  shelf  or 
counter  in  front  of  the  switch  are  used  for  testing.  They  are  pro- 
vided with  flexible  connections  and  wedges  (280),  so  that  they  can 
be  thrown  into  the  circuit  of  any  desired  line  at  a  moment's  notice. 

287.  Instrument  Tables. — In  most  large  stations,  the  different 
sets  of  apparatus  are  arranged  in  groups  of  four,  upon  tables  about  4 
by  6  feet,  divided  by  two  vertical  intersecting  screens  into  four  sec- 
tions, each  accommodating  a  complete  set  of  instruments,  sounder, 
relay,  and  key.      A  group   of  4  pairs  of  instrument  wires  extends 
from  the  switchboard  to  each  table,  and  a  second  group  of  4  pairs  of 
local  wires  extends  from  each  table   to   the   local  batteries.      The 
wires  are  usually  insulated  with  a  double  coating  of  gutta-percha,  and 
are  then  laid  up  in  cables  and  bound  with  tarred  tape.     It  was  for- 
merly the   practice  to  group   a  number  of  local   circuits  together, 
using  a  common  return-wire  for  the  group.     Experience  has  shown 
that  this  arrangement  is  objectionable,  and  that  it  is  better  to  keep 
all  the  circuits,  main  and  local,  of  each  line,  distinct  from  those  other 
lines  in  the  same  station. 

288.  The  Lightning  Arrester.— This  is  a  term  applied  to  all 
devices  employed  in  connection  with  telegraphic  apparatus  for  pre- 


77/^  Plate  Lightning  Arrester.  161 

venting  danger  of  injury  to  the  instruments  and  operators  by  atmos- 
pheric electricity,  and  from  the  powerful  currents  employed  in  elec- 
tric lighting,  which  sometimes  find  their  way  into  telegraphic 
conductors.  Atmospheric  electricity,  being  of  enormous  potential, 
will  take  a  short  route  through  a  poor  conductor,  or  even  through  a 
non-conductor,  in  preference  to  a  longer  one  through  a  better  con- 
ductor, while  the  reverse  is  true  in  respect  to  the  currents  of  com- 
paratively great  volume  and  low  potential  employed  in  telegraphy. 

289.  The  Plate  Lightning  Arrester. — A  common  form  has  a 
flat  brass  plate  connected  with  the  ground  wire.     Other  plates  of  brass 
which  rest  upon  this  are  electrically  separated   therefrom  by  thin 
sheets  of  non-conducting  ma- 
terial, or  by  the  air.     Each 

of  the  smaller  plates  is  pro- 
vided with  one  or  more 
binding  screws  for  the  at- 
tachment of  the  line-wires. 
Accumulations  of  atmos- 
pheric electricity  upon  the 
lines  usually  break  through 

the     insulating     material     to  FIG.  140.     Plate  Lightning  Arrester. 

the    ground-plate,    and    are 

thus  discharged  into  the  ground  without  injuring  the  apparatus.  Fig. 
140  shows  one  of  the  most  common  forms.  The  ground  wire  is  con- 
nected to  the  upper  plate  by  the  binding  screw  shown  at  the  left,  and 
the  line-wires  through  the  smaller  transverse  plates  beneath.  The 
confronting  faces  of  the  plates  are  surfaced  with  V-shaped  grooves, 
which  have  been  found  by  experience  to  facilitate  the  discharge  of 
lightning.  The  lightning  arrester  is  often  combined  with  the  switch- 
board, examples  of  which  construction  may  be  seen  in  Figs.  127  and 

131- 

290.  The  Safety  Fuse. —  Another  very  effectual  means  of  pro- 
tection consists  in  interposing  3  or  4  inches  of  the  thinnest  copper 
wire  which  can  be  procured  (say  No.  36)  in  each  circuit  between  the 
line  and  the  instrument.      An  abnormal  current,  whether  arising  from 
atmospheric  disturbances  or  from  contact  with  electric  lighting  or 
power  circuits,  instantly  fuses  the  thin  wire,  interrupting  the  circuit, 
and  thus  effectually  protecting  both  the  operators  and  the  apparatus 
This  device,  of  course,  requires  careful  attention,  inasmuch  as  it  is 
necessary  to  replace  the  fuse-wire  after  the  disturbance  has  ceased. 

291.  Inspection  and  Care  of  Arresters. — Care  should  be 
taken  to  keop  lightning  arresters,  especially  those  of  the  plate  pat- 


1 62      Equipment  of  American  Telegraph  Lines. 

tern,  free  from  dirt  and  moisture.  Neglect  of  this  precaution  is 
liable  to  cause  serious  interruption  of  communication.  A  discharge 
of  atmospheric  electricity  often  forms  a  permanent  connection  be- 
tween the  line  and  ground  plates.  Hence,  arresters  should  be  fre- 
quently taken  apart  and  examined,  and  this  should  especially  be 
attended  to  immediately  after  a  thunder-storm. 

292.  The  Repeater. — When  the  length  of  a  telegraphic  circuit 
exceeds  a  certain  limit,  dependent  upon  the  ratio  of  its  insulation  to 
its  conductivity  resistance,  the  working  margin    (220)  becomes  so 
small  that  satisfactory  signals  cannot  be  transmitted,  even  by  the 
aid  of  increased  battery-power.     This  limit,  under  the  existing  con- 
ditions of  insulation,  is  much  less  in  wet  weather  than  in  fine. 

Under  such  conditions,  it  was  formerly  necessary  to  retransmit  all 
communications  at  some  intermediate  station,  but  this  duty  is  now 
usually  performed  by  the  repeater.  This  is  simply  an  organized  ap- 
paratus, in  which  the  sounder  (or  in  some  cases  the  relay),  receiving 
the  signals  through  one  circuit,  opens  and  closes  the  circuit  of  an- 
other line,  in  the  manner  that  a  relay  opens  and  closes  the  local  cir- 
cuit of  a  sounder  (261).  The  repeater  is  also  used  to  connect  one 
or  more  branches  with  the  main  line,  for  the  purpose  of  receiving 
press-news,  etc.,  simultaneously  at  widely  separated  points.  Under 
these  conditions  the  stations  in  connection  may  correspond  with 
each  other  as  readily  as  if  all  were  upon  the  same  circuit.  By  mak- 
ing use  of  repeaters  it  is  quite  practicable  to  telegraph  direct,  when 
required,  between  places  situated  at  distance  of  several  thousands  of 
miles  apart. 

293.  Manual  and  Automatic   Repeaters. — The  different 
repeaters  which  have  been  devised  are  almost  innumerable.     They 
may,  however,  be  classified  as  manual  and  automatic.     The  manual 
repeater  is  usually  employed  for  temporary  purposes,  as  it  requires 
the  constant  attendance  of  an  operator  to  maintain  the  connections 
of  a  switch,  in  accordance  with  the  direction  in  which  the  communi- 
cation is  passing.     At  repeating  stations  where  a  permanent  service 
is  maintained,  the  automatic  repeater  is  employed,  which  requires 
no  supervision,  other  than  that  necessary  to  insure  the   apparatus 
being  kept  in  proper  adjustment. 

294.  The    Button    Repeater. — A  form  of  manual    repeater 
much  used  is  shown  in  diagram  in  Fig.  141.     It  is  known  as  the 
button  repeater.     The  western  main  line,  after  traversing  the  coil  of 
the  relay  M1,  passes  through  the   contact-points   of  armature   of 
sounder  S2  (the  movements  of  which  are  controlled  by  relay  M2)  and 
thence  to  main  battery  B1,  the  opposite  pole  of  which  is  connected 


The  Button  Repeater. 


163 


to  ground.  In  like  manner  the  eastern  line  traverses  the  coil  of 
relay  M2  and  the  contact-points  of  sounder  S1  and  to  battery  B2  and 
ground.  It  is  necessary  to  provide,  in  addition,  means  for  u  cutting 
out,"  or  closing  the  circuit  around  the  breaking-points  of  each 
sounder,  otherwise  the  apparatus  will  be  inoperative.  For  example, 
suppose  the  eastern  line  to  be  opened  by  the  key  of  the  operator. 
This  allows  the  armature  of  relay  M2  to  fall  off,  opening  sounder  S2, 
breaking  the  circuit  of  the  western  main  wire  at  its  contact-points. 
This  causes  the  armature  of  relay  M2  to  fall  off,  followed  by  that  of 
sounder  S1,  and  breaking  the  circuit  of  the  western  line  also.  The 


operator  of  the  eastern  line  cannot  now  close  the  circuit,  because  it 
is  still  open  in  another  place,  viz.,  at  the  contact-points  of  sounder 
S1.  The  switch  shown  at  L,  technically  termed  the  button,  removes 
this  difficulty,  for  when  it  is  swung  to  the  right  it  closes  a  spring- 
contact  C1,  forming  a  connection  between  the  contact-points  of 
sounder  S1,  enabling  the  operator  of  the  eastern  line  to  open  and 
close  its  circuit  at  pleasure,  while  his  signals  are  repeated  into  the 
western  line  by  the  action  of  the  contact-points  of  sounder  S2.  The 
switch  or  button  shown  at  L  in  the  diagram,  consists  of  two  pairs  of 
contacts  C1  and  C2,  normally  closed  by  a  spring  action,  one  pair  or 
the  other  being  separated  as  the  handle  L  is  moved  to  the  right  or 
left.  If  the  handle  remains  in  the  center,  both  sets  of  contacts  are 


164      Equipment  of  American  Telegraph  Lines. 

closed  and  the  eastern  and  western  lines  are  entirely  independent 
of  each  other. 

295.  Wood's  Repeater. — Another  form  of  button  repeater, 
known  as  Wood's,  is  illustrated  in  Fig.  142.  In  addition  to  the 
functions  performed  by  the  apparatus  last  described,  means  are  here 
provided  for  joining  the  two  lines  through  in  one  circuit  without  re- 
peating. The  apparatus  of  the  button  is  shown  in  full,  with  the 
instruments  and  batteries,  etc.,  in  outline  for  convenience  of  expla- 
nation. M1  and  M^  are  the  eastern  and  western  relays,  S1  and  S2 
the  eastern  and  western  sounders.  The  local  connections  are  omitted 


FIG.  142.     Wood's  Repeater. 

o  avoid  multiplicity  of  lines,  but  are  run  as  usual.  The  eastern 
and  western  main  batteries  at  E2  and  E1  have  opposite  poles  to 
ground  at  the  repeating  station,  so  that  when  the  lines  are  connected 
through,  the  two  batteries  will  coincide.  The  following  results  may 
be  obtained  with  this  apparatus : 

(i.)  Two  independent  circuits. — The  lever  L  remains  in  the  position 
shown  in  the  figure  marked  i,  i,  and  the  peg  at  4  inserted. 

(2.)  A  through  circuit. — The  lever  L  as  before,  but  the  peg  at 
4  open,  interrupting  the  ground  connection  between  the  batteries  B 
and  B1. 

(3.)  Two  independent  circuits  arranged  for  repeating. — The  peg  at 
4  is  inserted.  If  lever  L  be  placed  in  the  position  indicated  by  the 
reference  figures  2,  2,  the  eastern  sounder  repeats  into  the  western 


The  Milliken  Automatic  Repeater.  165 

circuit.     If  the  lever  is  shifted  to  3,  3,  the  western  sounder  repeats 
into  the  eastern  circuit. 

296.  Management  of  Button  Repeater. — The  duty  of  an 
operator  in  charge  of  the  button  repeater  is  very  simple.  He  has 
only  to  keep  the  relays  properly  adjusted,  and  when  he  hears  either 
sounder  fail  to  work  in  unison  with  the  other,  to  instantly  reverse 
the  position  of  the  lever  L. 


FIG.  143.      Milliken's  Repeater. 


297.  The  Milliken  Automatic  Repeater. — This  may  be 
considered  the  standard  repeater  of  the  United  States,  although 
many  others  have  obtained  more  or  less  acceptance.  All  automatic 
repeaters  embody  one  essential  principle,  which  is  this :  The  move- 
ment of  the  lever  of  the  relay  or  sounder  on  the  receiving  side  of 
the  apparatus  brings  into  action  some  device  for  bridging  the  con- 
tact-points of  the  opposite  sounder,  before  breaking  the  main  circuit 
on  the  second  line.  This  is  usually  effected  by  some  form  of  spring- 
contact,  although  there  are  different  ways  in  which  s-uch  a  device 
can  be  applied  to  produce  the  result  sought  for.  The  principle  of 


1 66      Equipment  of  American  Telegraph  Lines. 

the  Milliken  repeater  is  shown  in  Fig.  143.  The  main  and  local  cir- 
cuits are  run  precisely  as  in  the  button  repeater  (141).  The  auto- 
matic device  for  closing  the  opposite  circuit  is  applied  to  the  contact- 
lever  of  each  of  the  relays ;  for  example,  the  relay  M1  has  a  supple- 
mentary local  magnet  L1,  the  armature  of  which,  falling  off  under  the 
action  of  its  retracting  spring,  prevents  the  armature  of  relay  M1  from 
likewise  falling  off,  because  its  spring  is  adjusted  to  a  stronger  ten- 
sion than  the  relay-spring.  The  local  magnet  L1  is  actuated  by  a 
local  circuit  which  is  controlled  by  a  contact-point  on  the  lever  of 
the  opposite  sounder  S2.  When  the  sounder  lever  falls  off,  it  first 
breaks  the  supplementary  local  circuit,  and  holds  down  the  armature 
of  the  opposite  relay,  just  before  the  main  circuit  through  that  relay 
is  broken.  This  postponement  of  the  breaking  of  the  main  circuit 
is  effected  by  the  spring-contact  on  the  sounder  lever.  Hence  in 
this  repeater,  the  apparatus  on  the  east  side  remains  quiet  while  the 
western  line  is  working  and  vice  versa.  The  Milliken  repeater  is 
provided  with  buttons,  not  shown  in  the  figure,  for  cutting  out  the 
contact-points,  so  that  the  two  lines  can  be  worked  separately,  as  in 
the  case  of  the  manual  repeaters. 

298.  Management  of  Automatic  Repeaters. — In  repeat- 
ing signals  from  one  circuit  to  another,  the  sounder-lever  which  car- 
ries the  contact-points  has  to  move  a  certain  distance,  after  the  cir- 
cuit of  the  first  line  is  closed,  before  it  can  close  the  circuit  of  the 
second  line.  This  occupies  a  definite  time,  so  that  the  duration  of 
the  current  or  length  of  each  signal  sent  forward,  is  shorter  than  that 
received  from  the  transmitting  station.  A  second  repeater  shortens 
the  signals  still  more,  so  that  ultimately  the  signals  may  fail  altogether. 
This  may  be  partially  remedied  in  practice  by  the  skill  of  the  send- 
ing operator,  who,  in  working  through  a  repeater,  should  transmit 
his  signals  moreyfrw/y,  as  it  is  termed,  that  is,  increase  the  duration 
of  the  key  contact  (374).  It  is  also  important  that  the  sounder 
levers  should  be  permitted  the  least  possible  movement  compatible 
with  the  proper  operation  of  the  spring  contact-points  and  with  con- 
venience in  reading.  The  armatures  of  the  supplementary  local 
magnets  seldom  need  adjustment  if  the  batteries  are  kept  in  good 
condition.  The  adjustment  of  the  relays  is  precisely  the  same  as  in 
ordinary  apparatus.  The  tension  of  the  retracting  springs  of  the 
sounders,  on  the  other  hand,  should  be  very  moderate,  just  enough 
to  raise  the  armature  when  released.  A  repeater  works  most  effi- 
ciently when  the  signals  have  what  is  termed  a  "  dragging  "  sound. 
When  interrupting  the  sender  through  a  repeater,  the  receiving  op- 
erator should  first  hold  his  key  open  for  two  or  three  seconds. 


Characteristics  of  the  Dynamo-Current.       167 

299.  The    Dynamo-Electric   Generator.— In  some  large 
telegraphic  stations,  where  the  number  of  lines  to  be  supplied  is  very 
great,  dynamo-electric  machines  have  been  substituted  for  batteries 
with  highly  satisfactory  results.     A  minute  description  of  the  differ- 
ent organizations  of  apparatus  or  plants  which  have  been  employed 
does  not  properly  fall  within  the  scope  of  the  present  treatise,  but 
the  following  explanation   may  suffice  to  render  the  principles  of 
operation  comprehensible. 

300.  Characteristics  of  the  Dynamo-Current. — The  theo- 
retical principle  of  the  dynamo  has  been  briefly  set  forth  in  a  fore- 
going chapter  (80).     From  the  explanation  there  given,  it  will  be 
understood  that  this  machine,   in  its   elementary  form,  produces  a 
series  of  waves  or  undulations  of  electromotive  force  of  alternating 
polarity.     Beginning  at  zero,  for  example,  the  e.  m.  f.  gradually  in- 
creases to  a  positive  maximum  ;  then  gradually  falls  to  zero,  then 
rises  again  to  maximum  negative,  then  falls  again  to  zero,  and  so  on 
indefinitely  in  the  manner 

graphically  represented  in     j^  jg^ 

*ig-  144.      such  a  condi-  ^  ^ 

tion    is    obviously  wholly  FlG<  I44    Alternating  Currenl. 

unsuited  for  the  tele- 
graphic service,  which  requires  a  normally  continuous  current,  of 
determinate  polarity  and  of  approximate  uniform  strength.  The  alter- 
nate pulsations  produced  by  the  revolutions  of  the  armature  are  there- 
fore rectified  by  means  of  a  device  called  a  commutator,  the  effect 
of  which  is  to  reverse  every  alternate  wave,  so  as  to  transform  the 
alternating  waves  into  a  series  of  waves  all  positive  or  all  negative, 
as  the  case  may  be.  If  the  armature  be  provided  with  two  coils, 
placed  at  right-angles  with  each  other,  so  that  one  is  in  a  position 
of  maximum  at  the  same  instant  the  other  is  in  the  position  of  mini- 
mum action,  and  the  two  effects  be  combined,  the  result  will  be  a 

current    which,     although 

•  -»  4  *3*      «j* 

FIG.  145.     Rectified  Alternating  Current.  B7  Pacing  a  considerable 

number  of  separate  equi- 
distant coils  upon  the  armature,  and  superposing  their  effects,  in 
the  manner  indicated  by  the  dotted  outline  at  the  left,  it  is  prac- 
ticable to  obtain  a  current  which  is  practically  constant,  and  is 
found  to  be  perfectly  well  adapted  for  telegraphic  purposes.  For 
this  reason  the  rotating  armature  coils  of  the  dynamos  employed  in 
telegraphy  are  divided  into  a  large  number  of  sections,  each  coming 


1 68      Equipment  of  American  Telegraph  Lines. 


successively  into  the  position  of  maximum  inductive  action  as  the 
armature  is  revolved. 

301.  The  Electro-Magnetic  Field. — In  the  theoretical 
dynamo  hereinbefore  described  (80),  the  magnetic  field  in  which 

the  armature  coils  revolve  is  formed 
by  permanent  magnets.  In  prac- 
tice, the  far  more  powerful  field 
produced  by  electro-magnetism  is 
for  many  reasons  preferable.  The 
electro-magnet  which  maintains  the 
field  may  be  excited  by  a  current 
traversing  a  shunt  or  branch  of 
the  armature  circuit  (140),  in  which 
its  helix  is  included,  from  which 
circumstance  such  a  machine  is 
termed  a  self-exciting  dynamo,  and 
specifically  a  shunt-wound  dynamo. 
Fig.  146  is  a  theoretical  diagram, 
and  Fig.  147  a  perspective  view 
of  a  shunt-wound  dynamo  such  as 
is  used  in  telegraphy.2 

302.  The  Commutator. — In 
the  theoretical  dynamo  (Fig.  26, 
p.  33),  it  will  be  observed  that  the 
armature  coils  terminate  in  two 
semi-cylindrical  metallic  segments 
carried  upon  the  shaft.  Two  sta- 
tionary metallic  collectors,  termed 

brushes,  are  made  to  rub  upon  the  segments  at  opposite  points  of  the 
circle  as  they  revolve,  the  whole  apparatus  being  termed  the  com- 
mutator. In  Fig.  146  there  are  a  considerable  number  of  segments 
corresponding  to  an  equal  number  of  armature  sections,  and  two 
brushes,  which  form  respectively  the  positive  and  negative  poles  of 
the  dynamo-electric  generator.  The  thick  black  line  in  Fig.  146 
represents  the  exterior  or  work  circuit.  The  shunt  circuit  for  ex- 
citing the  field-magnet  is  shown  by  a  thin  line,  the  extremities  of 
which  are  likewise  united  to  the  respective  terminals  or  brushes. 
The  direction  in  which  the  currents  flow  in  both  the  main  and  shunt 
circuits  is  denoted  by  arrows. 

a  This  particular  machine  is  known  as  the  "  Edison  No.  2."  It  is  run  at  a  speed 
of  1200  revolutions  per  minute,  and  has  a  capacity  of  about  40  amperes.  The  resist- 
ance of  the  armature  is  about  0.1  ohm  and  of  the  field-magnet  coil  about  30  ohms. 


FIG.  146.     Circuits  of  Shunt  Dynamo. 


Characteristics  of  the  Dynamo.  169 

303.  Characteristics  of  the  Dynamo. — Each  dynamo,  when 
driven  at  a  definite  and  uniform  speed,  maintains  a  practically  uni- 
form difference  of  potential  (143)  between  its  terminals  or  brushes, 
which  is  dependent  upon  the  original  construction  of  the  machine. 
This  corresponds  to  the  difference  which  is  maintained  between  the 
poles  of  a  voltaic  element,  and  is  due  to  the  e.  m.f.  of  the  machine, 
or  of  the  cell,  as  the  case  may  be.  The  especial  advantages  of  the 


FIG.  147.      Perspective  View  of  Shunt- Wound  Dynamo. 

dynamo  over  the  voltaic  battery  are:  (i)  its  small  internal  resist 
ance  (131)  and  consequent  capacity  to  feed  a  very  large  number  of 
separate  lines  without  interference,  and  (2)  its  economy,  both  in 
space  occupied  and  in  cost  of  maintenance,  in  case  the  number  of 
wires  to  be  supplied  is  large. 

304.  Dynamos  in  Potential  Series. — In  a  large  telegraph 
station  the  different  lines  necessarily  vary  greatly  in  their  length  and 
resistance,  but  it  is  nevertheless  requisite  that  the  same  quantity  of 
current  should  be  as  nearly  as  possible  supplied  to  each.  This 
renders  it  necessary  that  the  electromotive  forces  applied  to  the  re- 
spective circuits  should  differ  accordingly.  This  is  effected  through 
the  agency  of  a  series  of  separate  dynamos  connected  together  upon 
the  same  principle  as  a  series  of  cells  in  a  battery  (132).  In  the 


170     Equipment  of  American  Telegraph  Lines. 


Western  Union  telegraph  station  in  New  York,  for  example,  there 
are  5  independent  dynamos  connected  in  a  series,  as  indicated  in  the 
diagram,  Fig.  148.  These  have  potentials  as  follows  :  A",  70  volts  ; 
B,  70  volts  ;  C,  60  volts  ;  D,  60  volts  ;  E,  65  volts.  One  terminal  of 
dynamo  A  is  connected  to  the  ground,  the  wires  i,  2,  3,  4,  and  5  are 


70 


SWITCHBOARD 


FIG.  148.     Dynamos  in  Potential  Series. 


led  to  corresponding  horizontal  bars  on  the  station  switchboard, 
from  the  point  of  connection  between  each  two  adjacent  dynamos  of 
the  series.  These  bars  are  respectively  termed  the  first,  second, 
third,  fourth,  and  fifth  potentials.  The  voltage  of  each  potential, 
and  the  average  resistance  of  the  individual  circuits  fed  therefrom, 
are  as  follows : 


No.  of  Potential. 

Volts. 

Average  Resistance 
per  Line. 

I 

70 

3000 

2 

140 

3500 

3 

200 

000 

4 

260 

5000 

5 

325 

5000 

As  the  different  lines  are  each  connected  to  one  of  the  vertical 
bars  on  the  switch  (Fig.  139),  of  which  there  may  be  any  number,  it 
will  be  easily  understood  how  any  line  may  be  supplied  with  the 
particular  potential  which  it  requires,  simply  by  pegging  it  to  the 
appropriate  horizontal  bar  upon  the  switchboard. 

305.  Positive  and  Negative  Dynamo  Series.— As  both 
positive  and  negative  potentials  of  the  various  voltages  are  required 
in  a  large  station,  two  separate  series  of  dynamos  are  employed,  sim- 
ilar to  that  shown  in  Fig.  148,  one  having  its  positive  and  the  other 
its  negative  terminal  to  the  switchboard  and  line.  A  third  series, 


Multiple    Telegraphy.  1 7 1 

of  similar  arrangement  and  capacity,  is  also  provided,  which  has  re- 
versing switches,  so  that  it  may  be  made  to  send  either  a  positive  or 
negative  current  to  line.  This  may  be  used  at  will  as  a  substitute 
for  either  of  the  two  regular  series  in  case  of  accident.  Each  series 
of  five  machines  is  driven  by  a  15  horse-power  steam-engine. 

306.  Arrangement  of  the  Shunt  Coils.— It  will  be  observed 
that  the  last  dynamo  E  in  the  series  (Fig.  148)  is  necessarily  called 
upon  to  furnish  less  current  to  the  lines  than  the  others.     The  sur- 
plus power  of  this  machine  is  therefore  utilized  with  advantage  to 
furnish  current  through  a  shunt  or  derived  circuit,  not  only  for  excit- 
ing its  own  field,  but  the  fields  of  all  the  other  machines  in  the  series. 
A  branch  or  derived  circuit  is  taken  from  each  terminal  of  this  ma- 
chine, and  the  field  coils  of  each  of  the  five  machines  of  the  series  are 
connected  across  from  one  branch  to  the  other  in  parallel,  as  shown 
by  the  thin  lines  in  Fig.  148,  so  that  each  receives  an  equal  portion 
of  the  branch  current. 

306  a.  Capacity  of  the  Dynamo  Generator. — A  plant  of  the 
capacity  of  that  which  has  been  described  can  be  made  to  furnish 
for  supplying  1000  lines,  and  yet  is  so  compact  that  it  may  be  in- 
stalled in  a  small  room. 

307.  Multiple  Telegraphy. — Within  thirty  years  from  the  first 
establishment  of  the  telegraph,  the  inconveniences  arising  from  the 
multiplication  of  wires  on  the   principal   commercial  routes  of  the 
United  States  proved  so  serious  that  it  became  urgently  necessary 
to  adopt  measures  of  relief.     The  effort  to  devise  an  effectual  remedy 
led  to  the  invention  of  systems  of  multiple  telegraphy,  in  which  the 
same  conductor  might  be  used  for  the  transmission  and  reception  of 
more  than  one  communication  at  the  same  time,  either  in  the  same 
or  in  opposite  directions.      The  most  generally  useful  of  these  have 
proved  to  be  those  which  have  been  termed  the  diptex,  which  trans- 
mits two  messages  in  the  same  direction  at  the  same  time  ;  the  con- 
traplex,  which  transmits  two  messages  in  opposite  directions  at  the 
same  time  ;  and  the  quadruple*,  which  is  capable  of  transmitting  two 
messages  in  each  direction  at  the  same  time.   .  The  contraplex  is 
more  generally  known  as  the  duplex. 

The  principle  which  is  common  to  all  these  systems  is  a  provision 
whereby  the  receiving  instrument  at  the  home  station,  while  free  to 
respond  to  the  signals  of  the  key  at  the  distant  station,  shall  not  re- 
spond to  the  signals  of  its  associate  key. 

308.  The  Differential  Electro-Magnet. — It  has  been  here- 
tofore explained  that  the  attractive  force  of  the  cores  of  an  electro- 
magnet depends  upon  the  ampere-turns  in  its  coil  (176),  that  is  to 


172      Equipment  of  American  Telegraph  Lines. 

say,  first,  upon  the  number  of  turns  in  the  magnetizing  helix,  and 
second,  upon  the  strength  of  current  in  amperes  traversing  the  wire. 
It  has  also  been  explained  that  the  polarity  of  the  core  is  determined 
by  the  direction  of  the  circulating  current  (168).  It  follows  from 
these  two  considerations,  that  if  two  currents  of  equal  quantity  are 
simultaneously  made  to  pass  in  opposite  directions  an  equal  number 
of  times  around  a  magnet  core,  they  will  neutralize  each  other's 
effect,  and  no  magnetism  can  be  developed  in  the  core.  An  electro- 
magnet of  this  kind  is  termed  a  differential  magnet. 

309.  Construction    of   Differential    Magnet.  —  There  are 
several  ways  in  which  a  differential  magnet  may  be  constructed,  all 
involving  essentially   the  same   principle.     Two  independent  wires 
must  be  provided  for  the  two  opposing  currents.     These  may  be 
wound  side  by  side  throughout  the  whole  length  of  the  helix  ;   they 
may  be  disposed  in  concentric  independent  helices  ;  one  helix  may 
be  wound  on  each  of  the  legs  of  a  U  magnet,  or,  what  is  perhaps 
most  commonly  done,  the  helices   may  be  divided   into  sections  by 
equidistant  non-conducting  planes  at  right-angles  to  their  axes,  and 
the  alternate  sections  connected  with  the  respective  circuits. 

310.  The  Single-Current  Duplex. — The  most  essential  parts 
of  the  apparatus  of  the  single-current  duplex  are  the  transmitter^  the 


FIG.  149. 


EARTH 

Single-Current  Duplex. 


differential  relay,  the  rheostat,  and  the  condenser.  Fig.  149  is  a  dia- 
gram of  the  apparatus  at  one  of  the 'two  terminal  stations.  The 
transmitter  D  is  virtually  a  key,  which  instead  of  being  actuated 
directly  by  the  ringer  of  the  operator,  receives  its  motion  from  the 
armature  of  an  electro-magnet  S  in  the  circuit  of  local  battery  L1, 
which  is  closed  and  broken  by  an  ordinary  key  K.  The  key-lever 


The  Single-Current  Duplex. 


/  o 


D  of  the  transmitter  has  a  spring  contact-lever  N  pivoted  at  n  and 
having  a  contact  9  which  normally  rests  upon  a  fixed  stop  ft,  from 
which  it  is  lifted  by  the  contact  0  each  time  the  key  K  is  depressed. 
The  differential  magnet  is  shown  at  M,  and  is  wound  in  either  of 
the  ways  heretofore  referred  to  (309)  with  two  wires,  but  otherwise 
does  not  differ  from  the  ordinary  single-wire  relay  (267).  The  actual 
construction  of  the  transmitter  is  best  seen  in  Fig.  150.  The  spring- 
contact  here  shown  differs  in  form,  but  not  in  principle,  from  that 


FIG.  150.     Single-Current  Transmitter. 

outlined  in  Fig.  149.  The  spring  in  this  instrument  is  carried  upon 
the  lever,  upon  a  little  insulating  pedestal,  and  normally  presses  up- 
ward against  a  stop  affixed  to  the  free  end  of  the  lever. 

When  the  armature  is  attracted,  the  opposite  end  of  the  lever  is 
raised,  and  the  free  end  of  the  spring  touches  the  adjustable  contact- 
stop  fixed  above  it  in  a  standard.  The  object  of  this  device,  as  will 
be  hereinafter  seen,  is  to  close  one  contact  before  breaking  the  other, 
or  in  other  words,  to  transfer  a  current  from  one  branch  of  the  cir- 
cuit to  another  without  interrupting  it. 

311.  Circuits  of  the  Single-Current  Duplex.  — Tracing 
the  circuit  of  the  line  entering  the  station  in  Fig.  149,  it  will  be  seen 
to  first  pass  through  one  wire  of  the  differential  relay  M,  entering  by 
wire  3  and  thence  going  by  wire  2  to  contact-lever  n,  and  thence 
through  stop  9  and  wire  6  to  the  earth.  Hence  currents  entering 
from  the  distant  station  will  actuate  relay  M  and  sounder  R,  pre- 


174      Equipment  of  American  Telegraph  Lines. 

cisely  as  in  the  open-circuit  system  ^212).*  If  now,  at  a  time  when 
no  current  is  coming  from  the  distant  station,  transmitter-lever  D  be 
depressed  by  the  closing  of  key  K,  the  terminal  of  main  battery 
B  will  be  brought,  at  the  point  o,  into  contact  with  spring-lever  N, 
and  will  almost  simultaneously  lift  it  from  point  h.  This  in  effect 
transfers  the  in-coming  line  from  the  ground-wire  6  to  the  battery- 
wire  i,  and  hence  a  current  will  rlow  through  wires  2  and  3  and  one 
coil  of  the  differential  magnet  m  to  the  line,  finding  its  way  to  the 
ground  at  the  distant  station.  But  it  will  furthermore  be  observed 
that  a  branch  leaves  the  line  at  the  point  #,  and  leads  by  way  of  wire 
4  through  the  opposing  wire  of  the  differential  magnet  M,  and  thence 
by  way  of  5  directly  to  the  earth  at  the  home  station.  Now  it  is  evi- 
dent that  the  outgoing  current  from  battery  B  must  divide  between 
the  two  branches  at  the  point  a  in  the  ratio  of  their  respective  resist- 
ances (134),  and  if  these  be  equal,  the  currents  must  necessarily  be 
equal  (140).  This  equality  of  resistance  is  effected  by  inserting  a 
rheostat  X1  (106)  of  german-silver  wire  into  the  branch,  so  as  to 
make  its  resistance  equal  to  that  of  the  line.  When  this  has  been 
done,  it  is  evident  that  the  outgoing  currents,  being  equal  and  oppo- 
site in  their  effects,  can  produce  no  magnetism  in  the  relay  M,  and 
hence  the  latter  cannot  respond  in  any  way  to  the  signals  of  its  asso- 
ciated key  K.  But  this  will  not  in  the  least  interfere  with  its  ca- 
pacity to  respond  to  the  action  of  currents  transmitted  by  the  distant 
key.  In  such  case  one  wire  of  the  relay  will  be  traversed  by  the 
current  due  to  the  conjoint  or  superposed  action  of  both  terminal 
batteries,  while  its  action  is  opposed  in  the  other  wire  of  the  relay 
only  by  the  current  of  the  home  battery.  The  incoming  current, 
therefore,  produces  upon  it  precisely  the  same  effect  as  if  the  current 
of  the  home  battery  were  not  present. 

312.  The    Artificial    Line. — The  branch    from    the    point  a 
through  4  and  5   to  the  earth  at   the   home  station,  is  termed  the 
artificial  line,  and  the  whole  problem  of  contraplex,  generally  termed 
duplex  telegraphy,  consists  in  simultaneously  reproducing  in  the  arti- 
ficial line,  as  nearly  as  may  be,  all  the  electrical  conditions  of  the 
external  or  working  line,  and  in  causing  them  to  act  in  an  opposite 
sense  upon  the  home  relay.     There  are  two  conditions  in  respect  to 
which  the  actual  line  is  subject  to  continual  variation,  viz.,  as  to  its 
resistance  (115)  and  its  electrostatic  capacity  (147). 

313.  Balancing   the   Resistance. — The  effect  of  imperfect 
insulation  upon  the  resistance  of  the  line  has  already  been  referred 
to  (242).     It  is  greatest  in  fine  weather  and  least  in  wet  and  foggy 
weather.     The  resistance  of  the  artificial  line  is,  however,  very  easily 


Electrostatic  Capacity  of  tke  Line.  i  75 


balanced ;  that  is,  adjusted  to  correspond  with  that  of  the  main  line 
by  plugging  or  unplugging,  as  required,  a  series  of  graduated  resist- 


FIG,  151.    [Resistance  Coils  of  Artificial  Line, 

ance  coils  of  german-silver  wire,  arranged,  as  shown  in   Fig.   151, 
upon  the  principle  explained  in  (106). 

314.  Electrostatic  Capacity  of  the  Line.— In  order  that 
the  process  of  adjusting  the  electrostatic  balance  of  the  artificial  line 
may  be  understood,  it    is    neces- 
sary first    to   explain    the    nature  l         l 
and  origin  of  the  corresponding 
phenomenon    as   exhibited   upon 
the  main  line. 


Whenever  electrical  generation  oc- 
curs, there  always   exists,  besides  a       EARTH  EARTH 
source    of    generation    at    which    the       FlG.  I52.    Recombination  of  Positive  and 
normal  equilibrium  is  first  disturbed,                        Negative  Electricity, 
(i)  certain  conditions  which  allow  the 

positive  and  negative  electricity  thus  separated  to  recombine,  or  else  (2)  cer- 
tain other  conditions  by  which  the  electricity  generated  is  accumulated  on 
two  surfaces  separated  by  a  medium  through  which  it  either  cannot  recom- 
bine, or  (3)  can  only  recombine  less  rapidly  than  the  source  can  generate.8 

3  F.  C.  WEBB  :  Electrical  Accumulation  and  Conduction  (part  i),  p.  2. 


i/6      Equipment  of  American  Telegraph  Lines. 

The  first  condition  referred  to  exists  in  the  case  of  a  cell,  or  series 
of  cells,  having  the  poles  joined  by  a  conductor  of  inappreciable  re- 
sistance (Fig.  152).  The  second  condition  exists  in  the  case  of  an 
insulated  telegraph  line  of  considerable  length,  connected  to  one 


3 


J 


FH;.  153.      Accumulation  of  Static  Electricity  upon 
EARTH  °Pen  Line- 

pole  of  a  grounded  battery  and  open  at  its  distant  end  (Fig.  153). 
The  third  condition  exists  when  the  line  assumed  in  the  last  case, 
instead  of  being  open  at  the  distant  end,  is  there  connected  to  the 
earth,  either  directly  or  through  an  instrument  or  other  appreciable 


EARTH  EARTH 

FIG.  154.    Accumulation  of  Electricity  upon  Line  to  Ground  at  Distant  End. 

resistance.      This  is   the   condition  of  a -duplex  telegraphic  circuit 
(Fig-  I54)-4 


«  These  figures  are  identical  with  those  which  have  heretofore  been  employed  in 
illustration  of  potential.     The  area  inclosed  between  the  base  line  and  the  line  of  po- 


Effect  of  Currents  of  Charge  and  Discharge.     1 77 

315.  Electrostatic  Accumulation  upon  Insulated  Con- 
ductor.— When,  therefore,  a  quantity  of  electricity  flows  through  a 
long  insulated  line,  the  electricity  which  constitutes  the  initial  por- 
tion of  the  current,  being  prevented  by  the  resistance  of  the  circuit 
from  recombining  instantaneously,  is  stored  up  or  accumulated  upon 
the  surface  of  the  conductor.     The  quantity  thus  accumulated  de- 
pends upon  the  diameter  and  length,  or,  in  other  words,  upon  (i) 
the  superficial  area  of  the  conductor,,  (2)  its  distance  from  the  earth, 
or  other  conductors  in  electrical  connection  with  the  earth,  and  (3) 

.  upon  the  character  of  the  insulating  medium  which  intervenes  be- 
tween it  and  the  earth.  Thus,  in  any  long  insulated  circuit,  a  certain 
portion  of  the  current  which  would  otherwise  reach  the  distant  sta- 
tion and  be  available  for  producing  signals,  is  abstracted  and  tied  up 
in  the  form  of  a  static  charge.  If  the  line  be  very  long  and  the  dura- 
tion of  the  current  be  very  short,  the  static  charge  may  absorb  the 
whole  of  it,  so  that  no  effect  will  be  appreciable  at  the  distant  sta- 
tion. As  the  static  charge  takes  up  the  initial  portion  of  every  cur- 
rent sent,  the  effect  is  the  same  as  if  its  appearance  at  the  distant 
station  were  retarded  or  delayed,  and  hence  the  apparent  velocity  of 
the  current  is  lessened.  The  initial  rush  of  current  into  the  line, 
sometimes  called  the  current  of  charge,  produces  for  an  instant  a 
much  more  powerful  magnetic  effect  upon  the  armature  of  the  relay 
than  does  the  permanent  current  which  continues  to  flow  after  the 
conductor  has  been  fully  charged.  The  momentary  effect  thus  pro- 
duced upon  the  relay  is  termed  by  the  operators  the  kick.  It  varies 
in  amount  with  the  electrostatic  capacity  of  the  line  ;  the  longer  the 
line  and  the  more  perfect  its  insulation,  the  higher  its  capacity  to  re- 
ceive charge  and  the  more  the  force  manifested  by  the  charging  cur- 
rent. 

316.  Effect  of  Currents  of  Charge  and  Discharge. — It 
will  therefore  be  understood  that  when  one  wire  of  a  differential  re- 
lay is  connected,  as  in   the  duplex  apparatus,  with  a  long  insulated 
line  having  a  considerable  electrostatic  capacity,  while  its  other  and 
opposing  wire  is  connected  with  an  artificial  line  principally  made  up 
of  a  rheostat  destitute  of  electrostatic  capacity,  although  the  resist- 
ances of  the  two  branches  may  be  exactly  the  same,  the  initial  charg- 

tential  may  be  correctly  taken  to  represent,  the  electrostatic  charge  in  each  case.  A 
consideration  of  Fig.  154  will  show  that  when  the  line  is  to  ground  at  the  distant  end, 
as  in  duplex  telegraphy,  75  per  cent,  of  the  aggregate  charge  of  the  line  is  accumu- 
lated upon  the  first  half  of  it,  and  only  25  per  cent,  upon  the  second  half.  Therefore 
the  currents  of  charge  and  discharge  are  three  times  as  great  at  the  battery  end  as  at 
the  ground  end.  This  is  upon  the  assumption  that  there  is  no  appreciable  loss  through 
imperfect  insulation. 


178     Equipment  of  American  Telegraph  Lines. 

ing  current  in  the  main  line  will  not  be  counteracted  by  a  corre 
spending  opposite  effect  in  the  artificial  line,  and  hence  a  momentary 
false  signal  will  be  produced  upon  the  home  relay.  So  also,  at  the 
termination  of  the  signal,  when  the  line  is  detached  from  the  battery 
and  connected  to  earth  at  the  home  station,  the  electrostatic  charge 
accumulated  upon  the  line  instantly  flows  back  to  the  ground  through 
the  rear  contact  of  the  transmitter,  passing  through  one  wire  only 
of  the  differential  relay,  and  another  false  signal  is  produced.  These 
false  signals,  occurring  at  the  beginning  and  end  of  each  true  signal 
sent  out  from  the  home  station,  if  not  eliminated,  would  mingle  with 
the  received  signals  from  the  distant  station,  and  utter  confusion 
would  be  the  inevitable  result. 

317.  The  Condenser. — This  difficulty  is  overcome  by  connect- 
ing to  the  artificial  line  a  device  termed  a  condenser,  which  consists 
of  a  large  number  of  sheets  of  tin-foil  connected  with  the  artificial 
line,  interleaved  with  an  equal  number  connected  with  the  earth,  and 
separated  by  sheets  of  insulating  material,  usually  mica  or  paraffined 
linen  paper.  By  arranging  these  sheets  in  separate  sections,  with 
proper  electrical  connections,  a  very  large  superficial  area  of  tin-foil 
is  exposed  to  inductive  action,  the  actual  extent  of  which  may  be 
varied  at  pleasure,  so  that  the  artificial  line  may  be  made  to  charge 
and  discharge  itself  at  the  same  instant,  and  to  the  same  extent,  as 
the  main  or  actual  line.  The  disturbing  effects  of  the  static  charge 
and  discharge  upon  the  differential  relay  may  thus  be  wholly  elim- 
inated.5 The  condenser  is  inclosed  in  a  wooden  box  and  provided 
with  a  peg  switch,  as  shown  in  Fig.  155,  so  that  its  electrostatic  ca- 
pacity may  be  varied  as  required. 

The  manner  in  which  the  condenser  is  connected  to  the  artificial 
line  and  to  the  earth  is  indicated  at  C  in  Fig.  149.  At  the  common 
point  5,  which  is  the  terminal  of  the  opposing  or  equating  coil  of  the 
differential  relay,  are  attached  the  rheostat  X1  (the  resistance  of 
which  is  maintained  equal  to  that  of  the  main  line),  and  the  con- 
denser C  (the  electrostatic  capacity  of  which  is  also  kept  equal  to 
that  of  the  main  line),  which,  by  their  joint  action  when  properly 
adjusted,  insure  a  perfect  working  balance  to  the  apparatus  under  all 
conditions. 

5  The  credit  of  the  idea  of  giving  to  the  artificial  line  of  the  contraplex  apparatus 
an  electrostatic  capacity  corresponding  to  that  of  the  main  line,  is  due  to  Joseph  B. 
Stearns,  who  successfully  applied  it  on  the  lines  of  the  Western  Union  Telegraph 
Company  leading  out  of  New  York,  in  1872.  By  this  admirable  application  of  a  scien- 
tific principle,  in  a  manner  no  less  ingenious  than  simple,  it  is  not  too  much  to  affirm 
that  the  commercial  value  of  the  aggregate  telegraphic  property  of  the  world  was  more 
than  doubled  at  a  single  stroke. 


The  Ground  and  Spark  Coils. 


179 


FiG.  155.     Adjustable  Condenser  of  Artificial  Line. 

318.  The  Ground  and  Spark  Coils.— It  is  necessary  that 
the  apparatus  at  the  home  station  should  always  present  an  equal 
resistance  to  the  currents  coming  from  the  distant  station,  so  as  not 
to  overthrow  the  balance  of  the  distant  relay.  This  is  effected  by 
means  of  small  rheostats  X1  and  X2  (Fig.  149),  termed  respectively 
the  ground-coil  and  the  spark-cot?,  the  resistance  of  the  former  being 
made  equal  to  that  of  the  latter,  plus  the  internal  resistance  of  the 
battery,  and  that  of  the  latter  being  sufficient  to  prevent  the  polariza- 
tion of  the  battery  when  momentarily  short-circuited  at  the  transmitter. 


FIG.  156.     Double-Current  Duplex. 


180     Equipment  of  American  Telegraph  Lines. 

319.  The  Double-Current  Duplex. — The  principle  of  this 
apparatus  will  be  understood  by  reference  to  Fig.  156.  Double  cur- 
rent or  reversing  keys  are  employed  at  each  end  of  the  line,  each  of 
which,  when  depressed,  reverses  the  poles  of  its  associated  main 
battery  without  interrupting  the  circuit,  and  of  course  without  chang- 


FIG.  157.      Polar  Relay 

ing  the  total  resistance.  Polar  relays  are  also  used,  the  peculiarity 
of  which  consists  in  the  employment  of  polarized  armatures,  the 
construction  and  use  of  which  have  been  explained  in  (200).  The 
actual  construction  of  the  polar  relay  is  shown  in  Fig.  157. 

The  permanent  magnetism  of  a  polarized  armature  causes  it  to 
remain,  by  its  own  attraction,  indifferently  in  contact  with  either 
pole  of  the  electro-magnet,  when  no  current  is  passing  through  its 


The  Double-Current  Duplex. 


181 


coils.  If,  then,  we  assume  this  electro-magnet  to  be  differentially 
wound,  and  the  armature  normally  at  rest  upon  the  rear  contact  so 
as  to  leave  the  local  circuit  open,  it  is  obvious  that  whether  the  cur- 
rent sent  out  from  the  associated  key  be  positive  or  negative,  it  can- 
not in  either  case,  owing  to  the  differential  action,  develop  any  mag- 
netism in  the  cores,  nor  alter  the  position  of  the  armature.  The 


FIG.  158.      Pole-Changing  Transmitter. 

differential  winding  therefore  produces  the  same  effect  with  the  polar 
as  with  the  neutral  relay.  But  at  the  distant  station,  the  currents 
received  over  the  line  traverse  one  wire  of  the  relay  only,  and  hence 
the  polarity  of  the  core  at  that  station  is  reversed  each  time  the 
sending  key  is  depressed  or  raised.  When  the  key  is  down,  a  posi- 
tive current  passes,  and  the  armature  closes  the  local  circuit ;  when 
it  is  up,  a  negative  current  passes,  and  the  local  circuit  is  broken. 
In  other  words,  the  signals  are  produced  by  changing  the  polarity  of 


1 82      Equipment  of  American    Telegraph  Lines. 

the  current,  and  not  by  changing  its  strength  from  zero  to  maximum, 
as  in  the  single-current  system.  The  actual  construction  of  the 
transmitter  employed  is  shown  in  Fig.  158. 

320.  The  Quadruplex. — This  apparatus  may  be  regarded  as  a 
combination  of  the  single-current  and  double-current  duplex  systems, 
adapted  to  be  operated  simultaneously  in  the  same  circuit.  It  has 
been  explained  that  the  polar  relay  in  the  double-current  duplex 
(319)  is  actuated  solely  by  changes  in  polarity,  irrespective  of 
strength,  and  in  the  single-current  duplex  (310)  solely  by  changes  in 
strength  of  current,  irrespective  of  polarity.  If  then  we  place  both 
a  polar  and  a  neutral  relay  in  series  in  the  same  circuit,  as  shown  in 
Fig.  159,  it  is  evident  that  we  may  produce  signals  by  moving  the 
armature  of  the  polar  relay  to-and-fro  by  means  of  alternate  positive 


LINE 


FIG.  159.     The  Diplex— the  Basis  of  the  Quadruplex. 

and  negative  currents,  and  in  case  these  are  not  strong  enough  to 
affect  the  armature  of  the  neutral  relay,  no  signals  will  be  indicated 
thereby.  So  also,  if  we  maintain  a  constant  polarity,  and  merely 
open  and  close  the  circuit,  we  shall  produce  signals  upon  the  neutral 
but  not  upon  the  polar  relay. 

321.  Principle  of  the  Diplex. — Fig.  159  is  a  diagram  show- 
ing a  line  having  at  one  terminal  station  two  keys,  one  single-cur- 
rent and  the  other  double-current  or  reversing.  The  battery  is  also 
in  two  sections,  one  section  B2  having  three  times  as  many  cells  and 
therefore  three  times  as  much  e.  m.f.  as  the  other  section  B1.  By 
tracing  the  connections,  it  will  be  observed  that  both  sections  of  the 
battery  are  included  in  a  loop,  the  terminals  of  which  are  reversed  by 
the  depression  of  the  key  K1,  but  that  the  greater  section  B2  of  the 
battery  only  comes  into  action  when  the  other  key  K2  is  depressed. 


Operation  of  the  Dip  lex. 


183 


Thus  it  is  obvious  that  the  e.  m.  f.  of  the  current  going  to  line  will 
be  four  times  as  great  when  key  K1  is  depressed  as  when  it  is  at 
rest,  and  that  the  key  K2  when  depressed  serves  to  reverse  whatever 
c.  m.  f.  may  be  in  circuit  at  the  moment,  whether  of  both  sections 
or  only  the  smaller  section  of  the  battery.  In  brief,  the  key  K1  con- 
trols the  polarity  of  the  outgoing  current  regardless  of  its  e.  m.f., 
while  key  K2  controls  the  e.  m.  f.  of  the  outgoing  current  regardless 
of  its  polarity. 

322.  Turning  now  to  the  receiving  apparatus,  we  have  in  series, 
at  the  receiving  end  of  the  same  circuit,  a  polar  relay  R1  and  an 
ordinary  or  neutral  relay  R~.     If  the  armature-spring  of  the  neutral 
relay  R2  be  adjusted  to  such  a  tension  that  it  cannot  respond  to  the 
comparatively  weak  current  of  the  battery  B1,  when  unassisted  by 
the  battery  B2,  it  is  obvious  that  signals  may  be  sent  by  reversing 
the  smaller  battery  section  by  means  of  the  key  K1,  which  will  act- 
uate  the   polar  relay  R1, 

but  will  produce  no  effect 
whatever  upon  the  relay 
R2.  On  the  other  hand, 
signals  may  be  sent  by  the 
key  K2,  each  depression 
of  which  throws  upon  the 
line  the  additional  e.  m.f. 
of  the  greater  battery  sec- 
tion B2.  The  additional 
strength  of  current  which 
now  flows  will  actuate  the 
neutral  relay  R2,  but  will 
produce  no  effect  upon 
the  polar  relay  other  than 
to  increase  the  pressure 
of  its  armature  against 
whichever  stop  it  may 
chance  to  be  in  contact 
with.  But  the  polarized 
armature,  on  the  other  FlG>  l6o> 

hand,  will  instantly  re- 
spond to  each  reversal,  whether  of  the  smaller  or  the  larger  current. 

323.  Operation  of  the  Diplex. — Suppose  a  signal  is  being 
sent  by  the  depression  of  key  K2 ;  both  sections  of  the  battery  are 
in  circuit  on  the  line,  causing  the  armature  of  the  neutral  relay  R2 
to  be  attracted.     If  now  another  signal  be  sent  by  the  depression 


L/N£ 

Receiving  Sounder  of  Diplex. 


184      Equipment  of  American  Telegraph  Lines. 

of  the  key  K1,  the  full  strength  of  the  current  traversing  the  neutral 
relay  R2  will  be  rmersed.  It  is  obvious  that  during  this  operation, 
no  matter  how  instantaneously  the  reversal  may  be  effected,  there 
must  be  an  interval  during  which  no  magnetism  is  manifested.  The 
actual  result  of  this  is  found  to  be  that  the  neutral  relay  lets  go  its 
armature  for  an  instant,  and  the  spring  begins  to  pull  it  away,  but  it 
scarcely  has  time  to  move  before  the  opposite  magnetism  seizes  upon 
it  and  restores  it  to  its  original  position.  This,  if  not  guarded 
against,  causes  a  slight  break  in  the  signal,  known  as  the  dip,  which 
may  nevertheless  be  eliminated  by  the  aid  of  special  devices. 

One  of  the  most  efficient  of  these  devices  is  that  of  an  interme- 
diate local  relay  interposed  between  the  neutral  main-line  relay  and 
its  associated  sounder  in  the  manner  indicated  in  Fig.  160.  When 
the  armature  of  the  neutral  relay  R  falls  off,  the  sounder  S  is  not 
affected  until  it  reaches  its  rear  contact-point,  when  it  closes  the  cir- 
cuit of  the  local  relay  L,  and  the  latter,  also  by  its  rear  contact, 
breaks  the  second  local  circuit.  When  the  main-line  is  closed  the 
reverse  action  takes  place.  Thus  the  sounder  can  only  be  affected 
by  a  full  opening  of  the  main  circuit,  which  shall  continue  long 
enough  to  permit  the  relay  armature  to  reach  in  rear  contact.  A 


FIG.  161.      Short-core  Neutral  Relay  for  Quadruple*- 

neutral  relay  having  very  short  cores,  as  in   Fig.    161,  is  for  this 
reason  advantageous  (195). 

324.  The  Diplex  and  Contraplex  Combined. — Having  an 
apparatus  of  this  kind,  capable  of  transmitting  two  sets  of  signals  in 
the  same  direction  at  the  same  time  without  interference  with  each 


Quadruple*  worked  by  Dynamo-Currents.      185 

other,  it  is  not  difficult  to  understand  that  by  applying  a  differential 
winding  to  both  relays,  polar  and  neutral,  and  by  including  both  in 
the  circuit  of  the  main  and  artificial  lines,  precisely  as  in  the  case 
of  the  single-current  and  polar  duplexes  (310,  319),  it  becomes  per- 
fectly practicable  to  transmit  two  sets  of  signals  upon  a  line  in  each 
direction  at  the  same  time,,  and  this  is  in  fact  precisely  what  is  done 
in  the  case  of  the  quadruplex.6 

325.  Quadruplex  worked  by  Dynamo-Currents.  —  The 
quadruplex  apparatus  at  the  larger  stations  in  the  United  States  is 
now  frequently  operated  by  dynamo-currents,  and  it  is  probable  that 
this  method  will  in  time  become  practically  universal.7  The  organi- 
zation of  the  apparatus  has  been  slightly  modified  from  that  illus- 
trated in  Fig.  159,  to  better  adapt  it  to  the  conditions  under  which 
it  is  required  to  work.  The  principle  will  be  understood  by  refer- 
ence to  Fig.  162.  D1  and  D2  represent  two  independent  series  of 
dynamos,  such  as  hereinbefore  described  (304),  one  having  its  posi- 
tive and  the  other  its  negative  pole  to  the  line.  K1  is  the  pole- 
changing  transmitter  and  K2  the  single-current  transmitter,  which, 
for  simplicity,  are  shown  in  the  diagram  as  keys,  but  which  are  in 
practice  operated  by  electro-magnets,  local  batteries,  and  independent 
keys,  as  indicated  in  Fig.  149.  When  the  apparatus  is  at  rest,  the 
current  from  the  negative  dynamo  D3  traverses  a  resistance  coil  of 
say  600  ohms  (which  is  inserted  to  avoid  danger  of  injury  to  the  in- 
struments in  case  of  an  accidental  short  circuit)  to  the  rear  contact 
of  the  pole-changing  key  K1 ;  thence  through  wire  i  (in  which  is  in- 
cluded a  rheostat  of  say  1200  ohms)  to  the  point  2,  where  it  divides 
into  three  portions ;  the  first  portion  going  to  the  line  and  distant 
station,  the  second  through  the  artificial  line,  including  rheostat  X, 
to  the  earth,  and  the  third  through  the  wire  3,  the  normally  closed 
rear  contact  of  the  single-current  key  K2,  and  a  rheostat  of  say  900 

8  The  method  of  diplex  transmission  here  described,  which  forms  the  basis  of  the 
commercial  quadruplex  system,  was  invented  in  1873  by  Thomas  A.  Edison  (see  U.  S. 
patent  No.  162,633,  APr-  27»  ^75)-  He  also  devised  the  apparatus  described  in  (323), 
to  overcome  the  principal  obstacle  in  applying  the  method  in  quadruplex  transmission. 

7  The  first  successful  application  of  the  dynamo  machine  as  a  substitute  for  the 
voltaic  battery  in  commercial  telegraphy  was  made  in  1879  by  Stephen  D.  Field  of  San 
Francisco.  (See  his  U.  S.  patents,  Nos.  223,845,  Jan.  27,  1880,  and  243,698,  July  5, 
1881.)  Detailefl  descriptions  of  some  of  the  more  important  dynamo  plants  have  been 
published  as  follows  :  Western  Union,  New  York,  Operator  and  Electrical  World, 
xiv.  225  ;  same  plant  improved,  W.  MAVER,  Jr.,  in  Electrical  World,  xi.  67,  79  ;  W. 
U.  plant,  Pittsburgh,  W.  MAVER,  Jr.,  ibid,  xii.  195  ;  W.  U.  plant,  Chicago,  ibid^  xv. 
173;  Postal  Tel.  Cable  Co.,  N.  Y.,  ibid,  xii.  65  ;  Postal  T.  C.  Co.,  Boston,  ibid,  xvi. 
313.  The  plant  of  fifteen  dynamos  in  the  Western  Union  N.  Y.  central  station  does 
the  work  of  more  than  30,000  cells  of  gravity  battery. 


1 86      Equipment  of  American  Telegraph  Lines. 

ohms,  to  the  earth.  If  for  example,  therefore,  we  assume  the  resist- 
ance of  the  main  and  artificial  line  to  be  3600  ohms  each,  it  follows 
from  the  law  of  distribution  of  currents  in  branch  circuits  (140),  that 


FIG.  162.     Quadruple!  Operated  by  Dynamo  Currents. 

two-thirds  the  current  will  return  to  earth  through  wires  3  and  4,  one- 
sixth  will  go  to  the  main  line,  and  one-sixth  to  the  artificial  line. 

326.  Distribution  of  Currents  in  Quadruplex  Apparatus. 
— If  now  the  key  K2  be  depressed  in  order  to  send  a  signal,  a  direct 
connection  will  be  formed  between  key  K1  and  the  point  2  through 


Practical  Management  of  the  Quadruple*.     187 

wires  5  and  3,  shunting  the  i2oo-ohm  coil  in  wire  i.  At  the  same 
time  the  wire  4  will  be  opened,  and  the  whole  current  will  divide  at 
the  point  2,  half  going  to  the  main  line  and  half  to  the  artificial  line. 
It  follows,  therefore,  that  with  the  several  resistances  in  the  ratios 
shown,  the  current  sent  to  line  by  the  key  K1  when  key  K2  is  de- 
pressed will  be  three  times  as  strong  as  when  the  latter  is  raised, 
and  this  will  be  equally  true  whether  the  current  sent  by  key  K1  be 
positive  or  negative. 

327.  A  computation  of  the  effects  of  the  several  resistances  will 
also  show  that  when   an  arriving  current  reaches  the  point  2,  the 
resistance  which  it  has  to  encounter  in  passing  thence  to  the  ground 
is  the  same,  whether  the  key  K2  be  depressed  or  raised.     When  the 
key  is  depressed,  the  resistance  is  only  that  of  one  or  the  other  of 
the   6oo-ohm  coils  between   the   key  K1  and  the   dynamos ;   when 
raised,  it  is  the  joint  resistance  of  one  coil  of  600,  plus  the  coil  of 
1200  (a  total  of  1800),  in  one  branch,  and  the  coil  of  900  in  the 
other  branch,  the  joint  resistance  of  the  two  being  600,  the  same  as 
in  the  first  instance.     The  relays  R1  and  R2  at  each  station,  being 
both  differential,  are  not  affected  by  outgoing  currents,  whatever  may 
be  the  strength  or  the  polarity  of  such  currents. 

328.  Practical  Management  of  the  Quadruplex. — Skill 
in  the  management  of  an  apparatus  of  so  much  complexity  as  the 
quadruplex  can  only  be  acquired  by  experience  and  careful  study. 
Only  a  few  hints  can  be  given  here.8     As  a  preliminary  to  these  sug- 
gestions, an. explanation  of  certain  technical  terms  which  have  come 
into  use  with  the  apparatus  is  necessary. 

The  "  No.  i  side  "  of  the  apparatus  comprises  the  pole-changing 
transmitter,  the  polar  relay,  and  their  attachments. 

The  "  No.  2  side  "  of  the  apparatus  comprises  the  single-current 
key,  the  neutral  relay,  and  their  attachments. 

The  tap-wire  is  the  intermediate  wire  which  divides  the  battery 
into  two  unequal  portions,  usually  termed  respectively  the  long  end 
and  the  short  end.  (See  Fig.  159.) 

The  resistance  which  is  inserted  to  compensate  for  the  internal 
resistance  of  the  battery  is  called  the  ground-coil.  A  resistance  x, 
Fig.  162,  is  also  placed  between  the  condenser  and  the  differential 

s  A  great  amount  of  information  of  value  respecting  the  history,  theory,  and  prac- 
tice of  quadruplex  telegraphy  may  be  found  in  a  series  of  articles  by  WILLIAM  MAVER, 
Jr.,  in  Electrical  World,  xi.  254,  266,  280  ;  and  in  a  subsequent  discussion  by  FRANCIS 
W.  JONES,  ibid,  xi.  290,  330,  xii.  276;  W.  MAVER,  Jr.,  ibid,  xi.  305,  xii.  231 ;  CLAR- 
ENCE L.  HEALY,  ibid,  xi.  292 ;  THOMAS  HENNING,  ibid^  xi.  330 ;  H.  W.  PLUM,  ibid, 
xi.  316.  See  also  F.  W.  JONES  :  The  Quadruplex,  Journal  Am.  Electrical  Soc.,  i.  16 ; 
F.  L.  POPE:  Quadruplex  Telegraphy,  The  Telegrapher,  xi.  271. 


1 88      Equipment  of  American  Telegraph  Lines. 

relays  on  long  circuits,  to  retard  the  time  occupied  in  the  charge  and 
discharge  of  the  condenser,  in  correspondence  with  that  of  the  line. 

The  proportion  between  the  long  and  the  short  end  of  the  battery 
varies  in  practice  with  the  length  of  the  line.  On  lines  of  100  miles 
or  less  the  division  is  usually  equal,  or,  as  it  is  termed,  2  to  i  ;  on  a 
line  350  or  400  miles,  it  may  be  with  advantage  as  much  as  4  to  i. 

329.  Adjustment  of  the  Apparatus. — The  following  method 
of  procedure  has  been  recommended  by  experienced  operators, 
though  it  is  proper  to  say  that  some  difference  of  opinion  exists  in 
reference  to  the  minor  details  of  adjustment. 

First.  Instruct  distant  station  to  "ground."  He  will  then  put 
the  line  to  ground  through  his  battery-compensation  resistance  or 
ground-coil.  Both  stations  should  assure  themselves  that  the  resist- 
ance of  the  ground-coil  is  equal  to  that  of  the  battery. 

Second.  The  line  being  to  ground  at  both  ends,  proceed  to  centre 
the  armature  of  the  polar  relay.  When  centred,  it  should  remain 
indifferently  in  either  an  open  or  closed  position  of  the  local  circuit 
as  placed  by  the  finger. 

Third.  Switch  in  the  home  battery,  and  vary  the  rheostat  resistance 
in  the  artificial  line  until  the  polar  relay  can  be  again  centred.  If 
disturbing  effects  from  foreign  currents  are  felt,  it  may  not  be  pos- 
sible to  do  this  accurately.  In  such  case,  approximate  it  as  nearly 
as  possible. 

Fourth.  Instruct  the  distant  station  to  switch  in  his  battery.  This 
may  assist  in  adjusting  the  polar  armature. 

Fifth.  Instruct  distant  station  to  close  both  keys,  thus  sending 
full  current  to  you.  Close  your  No.  2  key  ;  send  dots  on  your  No. 
i  pole-changer,  and  alter  the  capacity  of  your  condenser  until  its 
effects  on  the  home  polar  relay  are  eliminated.  This  condition  is 
termed  the  electrostatic  balance. 

Sixth.  After  both  stations  have  thus  balanced,  test  the  correct- 
ness of  the  adjustments  as  follows : 

Instruct  distant  station  to  send  dots  on  No.  i  and  words  on  No. 
2.  While  this  is  being  done,  alternately  open  and  close  both  keys 
at  the  home  station.  If  both  sets  of  signals  from  distant  station 
come  distinctly  under  all  circumstances,  the  balance  is  obviously  cor- 
rect. The  same  test  should  be  repeated  by  the  distant  station,  in 
order  to  ensure  an  accurate  working  adjustment. 

In  the  above  test,  if  the  sending  on  No.  2  side  should  fail  to  come 
well,  instruct  distant  station  to  hold  No.  i  key  open  for  a  few 
seconds,  and  then  closed  the  same  length  of  time.  If  the  signals 
come  imperfectly  in  both  cases,  it  indicates  that  the  contact-points 


Repeaters  for  Multiple    Telegraphy.  189 

of  the  distant  pole-changer  require  cleaning.  A  very  fine  flat  file 
is  the  proper  tool  to  use  for  this  purpose. 

If  the  dots  on  No.  i  fail  to  come  well  at  the  same  time  with  the 
writing  on  No.  2,  instruct  distant  station  to  alternately  open  and  close 
No.  2  key  at  intervals  of  a  few  seconds ;  the  trouble  may  usually  be 
traced  to  defective  contacts  upon  the  single-current  transmitter,  pro- 
vided the  balance  has  been  properly  attended  to. 

It  should  not  be  forgotten  that  a  change  of  weather  which  is  suffi- 
cient to  affect  the  insulation  of  the  line,  may  necessitate  a  readjust- 
ment, to  a  greater  or  less  extent,  of  both  the  rheostat  and  condenser 
balance  of  the  quadruplex.  Both  the  line  resistance  and  the  elec- 
trostatic capacity  are  diminished  by  a  defective  state  of  insulation. 

The  difficulties  which  may  arise  in  the  operation  of  a  quadruplex 
apparatus  are  of  such  various  character  that  it  would  be  quite  impos- 
sible to  enumerate  them  in  detail.  Those  which  have  been  referred 
to  are  among  those  most  liable  to  occur  under  ordinary  circum- 
stances. 

3290.  Repeaters  for  Multiple  Telegraph  Systems. — Not- 
withstanding the  apparent  complexity  of  the  duplex  and  quadruplex 
apparatus,  the  arrangement  of  repeaters  in  connection  with  them  is  a 
very  simple  matter.  It  is  only  necessary  to  include  the  electro-mag- 
net which  works  the  transmitter  of  one  line  of  communication  in  the 
same  local  circuit  with  the  receiving  apparatus  of  another  line  of 
communication.  This  facility  of  adaptation  of  repeating  devices 
gives  great  flexibility  to  the  system,  and  enables  it  to  be  employed 
for  special  service  in  a  great  variety  of  ways.  Thus,  for  example,  a 
single  wire  might  be  used  as  a  duplex  between  New  York  and  Boston, 
New  York  and  Hartford,  and  Hartford  and  Boston.  The  local  cir- 
cuits of  the  transmitter  and  of  the  receiver  in  a  main  office  may  be 
extended  through  several  branch  offices  in  the  same  city,  and  thus 
all  these  branch  offices  may  exchange  messages  directly,  either  with 
a  distant  main  station,  or  with  any  one  of  a  similar  group  of  branch 
offices  in  the  distant  city.  The  limits  of  the  present  work  will  not 
permit  a  detailed  description  of  these  various  applications  of  the 
system,  with  their  numerous  modifications,  but  the  general  principle 
will  be  readily  comprehended  by  those  who  have  made  themselves 
familiar  with  the  apparatus  on  which  they  are  based. 


CHAPTER    IX. 

TESTING    TELEGRAPHIC    LINES. 

330.  Object  of  the  Tests. — Telegraphic  lines,  from  their  ex- 
posed situation,  are  peculiarly  subject  to  interferences  and  interrup- 
tions from  various  causes,  and  hence  one   of  the   most  important 
duties  of  an  operator  is  to  familiarize   himself  with  .the  nature  of 
these  disturbances,  so  that  their  locatibn  may  be  quickly  determined 
and  the  proper  measures  taken  for  their  removal.     This  is  effected 
by  an  experimental  investigation,  technically  termed  testing.    Another 
object  in  testing  is  to  examine  the  electrical  condition  of  the  wires 
at  stated  intervals,  and  thus  detect  incipient  faults  before  they  be- 
come serious  enough  to  cause  interruption  of  the  service. 

331.  Faults  and  Interruptions. — The  principal  sources  of 
interruption  may  be  classified  as  follows : 

(0)  Disconnection  or  Break. — The  continuity  of  the  circuit  is  in- 
terrupted. A  break  may  give  rise  to  three  different  conditions : 
(i)  When  neither  of  the  broken  ends  is  in  electrical  connection  with 
the  earth;  in  this  case  the  circuit  is  wholly  interrupted  so  that  no 
current  can  pass  ;  (2)  when  one  end  is  in  connection  with  the  earth  ; 
in  this  case  there  is  no  current  on  the  portion  of  the  line  which  is 
disconnected  from  the  earth,  but  more  or  less  on  the  other  portion  • 
and  (3)  when  both  ends  are  in  connection  with  the  earth,  in 
which  case  there  will  be  more  or  less  current  on  both  sections  of 
the  line. 

(b)  Partial  Disconnection,   or  Resistance. — This    fault  may  arise 
from  unsoldered  and  rusty  joints  in  the  line-wire  ;  from  loose  connec- 
tions in  the  offices,  or  about  the  instruments,  switches,  and  batteries ; 
or  from  a  defective  or  insufficient  contact  between  the  earth-plate 
and  the  earth. 

(c)  Escape. — Leakage  from  the  line  to  the  ground  arising  from 
defective  insulation  generally,  or  specifically  from  the  line  getting 
into  contact  with  trees,  wet  buildings,  etc.     When  an  escape  is  so 
serious  that  it  is  impossible  to  work  past  it,  it  is  called  a  dead  ground. 

(d)  Cross. — This  term  is  used  to  denote  a  leakage  or  escape  of 
current  from  one  wire  into  another.     An  absolute  contact  between 


Testing  for  Disconnection. 


191 


two  or  more  wires,  so  tli.it  current  passes  freely  from  one  to  the  other, 
is  termed  a  metallic  cross.  Sometimes  parallel  wires  on  the  same 
supports  swing  to  and  fro  in  the  wind,  occasionally  touching  each 
other,  and  causing  an  intermittent  disturbance  termed  a  swinging- 
cross.  When  only  a  portion  of  the  current  passes  from  one  wire  to 
the  other,  through  defective  insulation,  wet  cross-arms  or  the  like, 
the  effect  is  termed  cross-fire,  or  sometimes  weather-cross  (248). 

A  defect  in  a  ground  wire  or  plate  which  serves  as  a  common  ter- 
minal for  two  or  more  lines,  produces  an  effect  similar  to  that  of  a 
metallic  cross.  This  difficulty  not  infrequently  arises  from  the  re- 
moval of  a  meter  in  the  line  of  a  gas-pipe  which  is  used  as  a  ground 
connection  for  the  wires  (210). 

332.  Testing  for  Disconnection.  —  When  the  circuit  of  a  line 
operated  on  the  American  or  closed-circuit  system  (214)  is  totally 


OOt ,   < rOO = — OO-x 

i  \  1+ 


FIG.  163.     Test  for  Disconnection. 

interrupted,  the  armature  of  every  relay  in  the  circuit  will  fall  off. 
In  such  case,  the  operator  at  each  way-station  should  immediately 
proceed  to  test  the  line  by  connecting  his  ground  to  the  line,  first  on 
one  side,  and  then,  if  necessary,  on  the  other,  as  has  been  explained 
in  a  previous  chapter  (278).  If  either  connection  closes  the  line,  the 
interruption  is  on  that  side,  for  the  circuit  of  the  opposite  terminal 
battery  is  completed  through  the  ground  in  place  of  the  interrupted 
wire.  If  the  ground-wire  gives  no  current  on  either  side,  it  is  most 
probable  that  the  trouble  is  in  the  testing-station,  though  it  may  be 
that  the  ground  connection  is  defective.  Each  operator  should  first 
assure  himself  by  a  careful  examination  that  the  fault  is  not  in  or 
about  his  own  apparatus.1  Having  ascertained  the  direction  in  which 
the  difficulty  lies,  he  should  at  once  report  the  facts  to  the  terminal 
station  at  the  opposite  end  of  the  line. 

1  An  easy  and  expeditious  way  of  doing  this  is  to  open  the  key,  and  then  slightly 
moisten  one  finger  of  each  hand  and  touch  lightly  the  binding-screws  by  which  the 
line-wires  enter  the  switch.  If  the  break  is  within  the  office  a  current  will  be  perceived 
by  the  touch. 


192  Testing   Telegraphic  Lines. 

Fig.  163  represents  a  line  with  four  stations,  A,  B,  C,  and  D.  If, 
for  example,  the  line  be  interrupted  by  a  break  at  JFt  two  operative 
circuits  may  be  formed  by  putting  on  the  ground-wires  at  B  and  C, 
as  shown  in  the  figure.  A  can  work  with  B,  and  C  with  Z>,  notwith- 
standing the  break  between  B  and  C. 

333.  Disconnection  is  usually  caused  either  by  the  breaking  of  the 
line-wire  or  else  by  the  careless  leaving  open  of  the  switch  of  a  key. 
Other  less  frequent  causes  are  wires  loose  in  their  binding-screws  (a 
defect  peculiarly  liable  to  occur  in  railway-station  offices,  on  account 
of  the  continual  vibration  caused  by  the  passage  of  trains),  defective 
switches,  and  breakage  of  the  fine  copper  wire  in  and  about  the  re- 
lay.    Sometimes  the  latter  is  burned  in  two  just  where  it  enters  the 
helix,  by  the  action  of  lightning. 

334.  Testing  for  Partial  Disconnection.— It  is  somewhat 
difficult  to  locate  this  fault  by  testing  merely  with  a  key  and  relay. 
It  is  liable  to  be  of  an  intermittent  character,  which  by  no  means 
tends  to  lessen  the  difficulty.     In  case  of  this  or  any  intermittent 
fault,  the  best  plan  is  to  cross-connect,  where  it  can  be  done,  by  in- 
terchanging the  defective  line  with  a  good  one  at  the  terminal  and 


x     r^x 


FIG.  164.     Test  for  Intermittent  Fault 

also  at  some  other  station,  as  in  Fig.  164.  If,  for  example,  the  fault 
is  at  F  on  No.  2  wire ;  by  cross-connecting  at  A  and  also  at  B,  as 
shown,  the  fault  will  shift  to  No.  i,  showing  it  to  be  between  the  two 
points  where  the  wires  were  to  have  been  interchanged.  If  it  were 
beyond  B  it  would  have  remained  on  No.  2  circuit.  In  the  latter 
case,  put  the  wires  straight  again  at  B,  and  cross-connect  at  C  and 
so  on,  station  by  station,  until  the  fault  shifts  to  No.  i,  which  proves 
it  to  be  between  the  two  last  stations. 

335.  Testing  for  Escape. — Call  the  stations  up  in  rotation, 
beginning  with  the  most  distant  one,  and  instruct  each  one  to  open 
his  key  for  say  ten  seconds.  When  any  station  beyond  the  point  of 
escape  is  open,  a  weak  current  will  nevertheless  pass  to  line  through 
the  home  relay,  the  circuit  being  partially  completed  through  the 
ground  by  the  fault.  For  example,  in  Fig.  165,  assume  that  terminal 
station  A  is  testing.  When  the  key  is  open  at  C  or  D  a  current  will 


Testing  for  a   Cross.  \  93 

pass  to  ground  through  the  point  ot  escape,  which  will  disappear  when 
JB  opens  his  key,  showing  the  fault  is  between  B  and  C. 

If  the  escape  is  so  serious  as  to  be  in-  effect  a  ground,  the  operator 
at  a  way-station  can  often  ascertain  in  which  direction  from  him  the 


r-00 


B  C 

-oo—  — * oo 


f- 


J. 1^^ 

FIG.  165.     Test  for  Escape. 

fault  is  located,  from  the  fact  that  it  cuts  off  or  perceptibly  weakens 
the  current  from  the  terminal  battery  in  that  direction,  when  tested 
with  the  ground-wire  by  the  aid  of  the  sense  of  feeling  in  the  finger 
or  tongue. 

336.  Testing  for  a  Cross. — In  case  a  cross  is  suspected  to 
exist  between  two  wires,  as  for  example  No.  i  and  No.  2,  instruct 
the  most  distant  station  to  open  No.  i,  and  send  dots  on  No.  2  wire. 
Then  open  No.  2  at  your  own  station,  and  if  the  dots  sent  on  No.  2 
at  the  distant  station  are  received  on  No.  i,  the  wires  obviously  must 
be  crossed.  Some  care  is  necessary  not  to  be  deceived  by  cross-fire, 
due  merely  to  imperfect  insulation,  and  not  to  actual  contact  between 
the  wires.  If  the  wires  are  in  actual  contact,  the  dots  or  signals  will 
come  nearly  as  strong  on  one  wire  as  on  the  other. 

Next,  instruct  the  distant  station  to  leave  No.  i  open.  Open  it  at 
the  home  station  also.  No.  2  will  now  be  free  from  interference,  and 
station^  maybe  communicated  with  upon  it  without  difficulty.  Com- 
mencing at  the  most  distant  station,  call  them  in  succession,  and  in- 
struct each  one  in  turn  to  send  dots  on  No.  2.  If  the  dots  come 
on  both  wires,  the  cross  is  between  the  home  station  and  the  sending 
station,  but  if  upon  No.  2  only  it  is  beyond  the  station  sending. 
Each  operator  along  the  line  should  be  instructed,  while  sending  dots 
on  one  wire,  to  open  the  other  wire,  if  practicable. 

337-  Principle  of  the  Cross  Test. — Figures  166  and  167  will 
explain  the  principle  of  this  test.  A  two- wire  line  is  represented 
having  four  stations,  A,  B,  C,  and  D.  Assume  the  operator  at  A  to 
be  testing  for  a  cross  which  is  located  between  B  and  C.  In  Fig. 
1 66,  No.  i  is  open  at  station  C  and  No.  2  is  open  at  station  A.  If 
C  sends  dots  on  No.  2  the  current  will  pass  over  to  No.  i  at  the 


i94 


Testing   Telegraphic  Lines. 


cross,  as  indicated  by  the  arrows,  and  the  dots  will  come  on  the  No.  i 
instrument  at  A,  showing  that  the  cross  is  between  A  and  C.  In 
case  C  is  not  able  to  open  No.  i,  the  result  will  evidently  be  the 
same,  provided  it  remains  open  at  D. 


FIG.  166.     Test  for  Cross. 

Now,  if  C  closes  both  wires  and  B  opens  No.  i,  and  writes  dots 
on  No.  2,  as  in  Fig.  167,  B  cannot  work  when  No.  2  is  open  at  A, 
as  both  wires  are  open,  one  at  A  and  the  other  at  B.  With  both 
wires  closed  at  A,  the  dots  which  B  sends  on  No.  i  will  reach  A  on 
No.  2,  the  current  from  F  going  over  both  the  wires  to  the  cross, 
and  from  thence  to  A  on  No.  2  alone.  Thus  the  cross  is  definitely 
located  between  B  and  C. 


FIG.  167.     Test  for  Cross. 

338.  A  convenient  and  expeditious  method  of  testing  for  crosses, 
in  offices  where  there  are  a  considerable  number  of  wires,  is  for  the 
operator  to  station  himself  at  the  switch  with  a  test  instrument,  as 
shown  in  Fig.  139.  When  any  station  has  been  instructed  to  send 
dots  on  some  particular  wire,  the  testing  operator  can  detect  them 
by  placing  one  finger  upon  the  ground-wire  and  the  other  upon  the 
line-wire  to  be  tested,  or  its  corresponding  bar  upon  the  switch.  In 
wet  weather,  however,  this  method  of  testing  is  sometimes  attended 
with  much  uncertainty,  as  it  is  extremely  difficult  to  distinguish  by 
this  means  between  the  effect  of  a  metallic  cross  and  those  due  to 
the  leakage  from  wire  to  wire  through  imperfect  insulation. 


The  Wheatstone  Bridge.  195 

339.  When  a  cross  is  found  to  exist  between  two  lines,  the  one 
having  the  largest  number  of  offices,  or  for  other  reasons  the  most 
available  for  business,  should  be  cleared.     The  remaining  wire  can 
then  be  utilized  for  a  considerable  portion  of  its  length,  by  instruct- 
ing the  stations  nearest  the  cross  in  each  direction  to  open  the  main- 
line wire  at  the  switch,  on  the  side  towards  the  cross  ;  ground  the 
other  side,  and  ground  the   line  in  the  other  direction.      This  will 
enable  the  second  line  to  be  utilized  in  two  sections. 

340.  Testing  by  Quantitative  Measurement. — The  tests 
which  have  been  thus  far  described  are  such  as  may  be  made  by  the 
ordinary   apparatus    employed    for    the    transmission    of  messages. 
They   serve  merely  to  roughly  indicate  the   nature  of  the  difficulty 
when  it  is  serious  enough  to  appreciably  interfere  with  correspond- 
ence, and  to  determine  between  which  two  neighboring  stations  it  is 
situated,  but  for  accurate  work  more  refined  methods  are  necessary. 
Galvanometers  and  rheostats  are  the  most  essential  instruments  em- 
ployed for  this  purpose,  and  the  results  are  deduced  by  computation 
from  actual   measurements,  made  upon   the  principles  which    have 
been  explained  in  Chapter  IV. 

The  measurements  required  are  principally  of  two  kinds  :  measure- 
ments of  resistance  and  measurements  of  quantity,  or,  as  it  is  usually 
termed,  current. 

341.  The  Wheatstone  Bridge. — This  apparatus  consists  of 
three  sets  of  resistance  coils,  a  galvanometer,  a  battery,  one  or  more 
keys,  and    the    necessary  connections.-      Its    principal    use    is    to 
measure   resistances,  which   may  be   done  by  its  means  with  great 
convenience   and  accuracy,  usually  from  o.oi   ohm  up  to    1,000,000 
ohms.     The  theoretical  arrangement  of  the  bridge  is  shown  in  Fig. 
1 68.     It  consists  of  four  resistances,  a,  b,  d,  and  x,  arranged  in  a 
parallelogram,  the  galvanometer  being  connected  across  one  trans- 
verse diameter,  and  the  battery  across  the  other.     When  the  values 
of  the  four  resistances  are  so  adjusted  in  relation  to  each  other  that 
the  current  from  the  battery  produces  no  deflection  upon  the  gal- 
vanometer, it  is  certain  that  these  several  values  must  then  bear  a 


1  This  ingenious  and  useful  system  of  electrical  measurement  was  first  described  by 
SAMUEL  HUNTER  CHRISTIE,  in  Phil.  Trans.  R.  S.,  1833,  95-142.  Its  importance  re- 
mained unappreciated  until  attention  was  directed  to  it  by  Professor  CHARLES  WHEAT- 
STONE,  in  a  lecture  before  the  Royal  Society  in  1843,  entitled  "  An  account  of  several 
new  Instruments  and  Processes  for  determining  the  Constants  of  a  Voltaic  Circuit." 
Phil.  Trans.  R.  S.,  cxxxiii.  303-327.  Although  full  credit  was  accorded  to  Christie  by 
Wheatstone  for  his  admirable  device,  electricians  have  ever  since  persisted  in  calling  it 
the  Wheatstone  Bridge,  and  it  seems  probable  that  it  will  always  continue  to  be 
known  by  that  name. 


Testing    Telegraphic  Lines. 


determinate  ratio  to  one  another.     This  ratio  may  be  expressed  as 
follows  : 

As  a  is  to  l>,  so  is  d  to  x. 

This  ratio  holds  good,  entirely  irrespective  of  the  magnitude  of 

any  of  the  resist- 
ances. In  the  actual 
apparatus,  therefore, 
as  used  in  practice, 
two  of  the  resistances 
(a  and  b)  are  fixed, 
and  the  third  (d)  ad- 
justable, the  fourth 
(x)  being  that  which 
is  to  be  determined. 
342.  Best  Ratio 
of  Electromotive 


FIG.  168.     Principle  of  Wheatstone  Bridge. 


Forces  and  Resistances.— In  performing  the  operation  of  test- 
ing, with  equal  resistances  in  the  branches  a  and  b  of  the  bridge,  the 
most  trustworthy  determinations  are  reached  by  preserving  a  due  re- 
lation between  the  value  of  the  e.  m.f.  employed,  the  branch  resist- 
ances a  and  b,  and  the  unknown  resistance  x,  which  is  to  be  meas- 
ured. Hence  when  the  unknown  resistance  is 

Between  I  and  100  units,  a  and  b  should  be  10  ohms  each ;  e.  /»./.,  i  volt. 
Between  100  and  1000,  a  and  b  should  be  100  ohms  each  ;  e.  m.  f.,  10  volts 
Between  1000  and  10,000,  a  and  b  should  be  1000  ohms  each  ;  c.  ///.  /.,  100 
volts. 

343.  Principle  of  the  Wheatstone  Bridge. — This  may  be 
most  readily  comprehended  by  considering  that  at  every  point  where 


100 


75 


50 


25 


120 


FIG.  169.     Fall  of  Potential  in  Arms  of  Bridge. 

a  circuit  divides  into  two  or  more  branches,  the  potential  of  each 
branch  must  necessarily  be  the  same.  If,  at  any  other  point,  any 
two  or  more  of  these  branches  are  again  joined,  the  potentials  must 
again  be  the  same.  In  the  bridge,  therefore,  if  we  assume  the  po- 
tential at  the  point  where  the  current  first  divides  to  be  say  100  volts, 


Principle  of  the  IVheatstone  Bridge.  197 

and  at  the  point  where  they  meet  again  or  are  connected  to  the  earth 
to  be  o,  let  each  circuit  be  assumed  to  be  divided  into  100  equal 
spaces,  as  indicated  in  Fig.  169.  If  now  a  wire  be  connected  across 
from  one  of  the  branch  circuits  to  the  other,  connecting  the  point  50 


FIG.  170.     Wheatstone  Bridge  Apparatus. 

to  50  or  75  to  75,  or,  as  shown  in  the  figure,  25  to  25,  or  between 
any  other  two  points  whatever  having  the  same  potential,  no  current 
can  flow  from  one  point  to  the  other  through  the  wire,  because  there 
exists  no  difference  of  potential  between  its  ends ;  but  if,  on  the 
other  hand,  the  wire  is  connected  between  any  two  points  of  different 


198 


Testing    Telegraphic  Lines. 


potential,  as,  for  example,  from  50  to  25,  a  current  will  necessarily 
flow  through  it  (143),  and  a  galvanometer  placed  in  the  wire  will  be 
deflected.  When,  therefore,  the  needle  is  not  deflected,  the  propor- 
tionality referred  to  in  (341)  must  always  exist  between  the  resist- 
ances of  the  four  sides  of  the  bridge.3 

344.  Actual  Construction  of  the  Bridge. — One  of  the  most 
useful  sets  of  coils  for  general  purposes  is  that  shown  in  Fig.  170, 

and  in  outline,  with  diagram 
of  bridge  connections,  in  Fig. 
171.  The  various  resistances 
are  arranged  in  the  manner 
hereinbefore  described  (341)  ; 
and  in  the  diagram,  Fig.  171, 
as  well  as  on  the  actual  box. 
the  respective  values  of  the 
resistances  are  denoted  by 
numbers  representing  ohms. 
The  points  marked  INF..  or 
"  infinite,"  indicate  a  total 
disconnection  when  the  plug 
is  withdrawn. 

In  some  of  the  more  mod- 
ern  sets   of  apparatus,   such 

as  that  shown  in  Fig.  172,  the  galvanometer,  rheostat,  branch-coils, 
contact-keys,  and  five  cells  of  battery,  with  the  necessary  connections, 
are  all  put  up  in  a  portable  mahogany  box,  with  lock  and  handle.  A 
lifter  is  provided  for  raising  the  needle  from  its  pivot  when  the  appa- 
ratus is  not  in  use. 

345-  Galvanometer  for  the  Wheatstone  Bridge.— In  se- 
lecting a  galvanometer  for  any  particular  purpose,  one  having  a 
few  turns  of  thick  wire,  and  small  resistance,  is  most  suitable  for 
measuring  small  resistances,  while  for  long  circuit  or  a  great  resist- 
ance of  any  kind,  a  galvanometer  of  many  turns  of  thin  wire  should 
be  selected.  Fig.  173  shows  an  excellent  type  of  galvanometer  for 
use  in  the  bridge  as  well  as  for  general  purposes.  It  has  an  astatic 
system  of  needles,4  suspended  by  a  delicate  silk  fibre,  and  is  fitted 

3  The  above  explanation  has  been  adapted   from   LATIMER  CLARK  :  Electrical 
Measurement,  p.  85.     The  student  desiring  to  acquaint  himself  thoroughly  with  the 
theory  of  the  bridge  may,  with  advantage,  consult  also  F.  JENKIN  :   Electricity  and 
Magnetism,  p.  241  ;  H.  R.  KEMPE  :  Handbook  of  Electrical  Testing,  p.  166  ;  SILVANUS 
THOMPSON  :  Elementary  lessons  on  Electricity  and  Magnetism,  p.  318. 

4  An  astatic  system  of  needles  consists  of  two  needles  suspended  parallel  to  each 
Other  and  near  together,  with  their  poles  placed  in  contrary  directions.     One  is  a  little 


FIG.  171.     Diagram  of  Bridge  Connections. 


Galvanometer  for  the  Wheats  tone  Bridge.     199 

with  a  permanent  magnet,  called  a  directing  magnet,  by  which  the 
needle  can  be  brought  to  zero  in  any  desired  angular  position  of  the 
apparatus. 


FIG.  172.    Wheatstone  Bridge  Apparatus,  with  Galvanometer  and  Battery. 

346.  To  Measure  the  Conductivity  Resistance  of  a 
Telegraph  Line. — Have  the  remote  end  of  the  line  put  to  ground, 
taking  care  that  no  relays  are  left  in  circuit.  Connect  the  home  end 

stronger  than  the  other,  so  that  the  pair  has  a  very  feeble  tendency  to  place  itself  in 
the  magnetic  meridian  (86  6).  Such  a  system  is  capable  of  being  deflected  by  a  very 
weak  current,  and  hence  is  used  in  th2  construction  of  the  more  delicate  types  of 
galvanometers. 


2OO 


Testing    Telegraphic  Lines. 


FIG.  173.     Astatic  Galvanometer  with  Directing  Magnet. 

of  the  line  to  the  terminal  C,  and  the  terminal  E  to  the  ground,  as 
in  Fig.  174.     Unplug  from  A  B  (b)  and  B  C  (a)  each,  a  resistance 

most  nearly  approx- 
imating in  value 
that  of  the  line  to 
be  measured  (342). 
Usually  this  will  be 
1000  in  each.  Press 
the  right-hand  or 
battery-key  B'  and 
remove  plugs  from 
E  A  (d)  until  the 
resistance  un- 
p  lugged  equals 
roughly  that  which 
is  to  be  measured. 
Then  depress  the 
left-hand  or  galva- 
nometer-key A',  and 

rearrange  and   adjust  the  plugs  in  E  A  (<i)  until  the  key  can  be 
repeatedly  opened  and  closed  without  causing  any  movement  of  the 


FIG.  174. 


EARTH 
Conductivity  Test, 


Conductivity  Resistance  by  Loop  Method,      201 

galvanometer-needle.5  When  this  balance  has  been  effected,  the 
resistance  unplugged  in  E  A  is  equal  to  the  conductivity  resistance 
of  the  line  under  test. 

346^.  Conductivity  Resistance  by  Loop  Method.— A  more 
accurate  method  of  making  conductivity  tests,  which  is  available 
whenever  there  are  three  or  more  parallel  wires  available  between 
the  same  points,  is  the  loop  test.  If  we  suppose  the  wires  to  be  Nos. 
i,  2,  and  3,  they  are  looped  together  in  different  combinations  at  the 
distant  station,  and  the  resistances  of  the  several  loops  taken  in 
succession,  one  end  of  the  loop  under  test  being  connected  to  C  and 
the  other  to  E,  as  in  Fig.  171.  For  example,  suppose  the  resistances 
to  measure  as  follows  : 

Resistance  of  I  and  2,  looped 6550  ohms. 

"  2  and  3,       "       6180      ': 

"  i  and  3,       "       6830      " 


Sum  of  all  three 19560      " 

As  by  this  process  the  resistance  of  each  wire  has  been  taken 
twice  over,  we  divide  the  amount  by  2  =  9780  ohms. 

If  we  deduct  from  this  result  the  total  of  each  pair  of  looped  wires 
in  succession,  the  remainder  in  each  case  must  be  the  resistance  of 
the  wire  not  in  the  loop.  Thus  : 

9780  —  6180  =  3600  for  No.  i  wire. 
9780  —  6830  ==  6830  for  No.  2  wire. 
9780  —  6550  =  3230  for  No.  3  wire. 

Conductivity  tests  may  also  be  made  with  sufficient  accuracy  fo? 
most  purposes,  and  with  great  convenience  and  facility,  by  means  of 
a  properly  constructed  voltmeter.  See  (369). 

347.  Earth  Currents. — In  making  conductivity  tests  with  the 
distant  end  of  the  line  to  ground  (346),  interference  is  sometimes 
caused  by  earth  currents,  which  flow  through  the  wire,  and  aid  or  op- 
pose the  testing  current,  as  the  case  may  be.  When  these  are  toler- 
ably steady  and  not  too  strong,  their  effect  may  be  eliminated  by 
making  measurements  with  both  a  positive  and  a  negative  current 
and  taking  the  mean  of  the  two  results.  Sometimes,  however,  these 
earth  currents  are  so  strong  that  an  accurate  measurement  cannot  be 
made,  and  the  loop  method  (3460)  must  be  resorted  to. 

6  Care  should  be  taken  in  all  cases,  when  finally  closing  the  circuit  by  the  second 
or  galvanometer-key,  to  first  make  very  short  contacts  or  "  taps,"  just  enough  to  indi- 
cate the  direction  of  the  deflection  of  the  needle,  until  the  coils  are  nearly  adjusted  to 
a  balance,  otherwise  much  time  will  be  needlessly  lost  by  the  oscillations  of  the  needle. 


2O2  Testing    Telegraphic   Lines. 

348.  Measurement  of  Resistance  of  Ground  Plate  at 
Distant  Station. — The  principle  of  this  measurement  is  the  same 
as  that  last  described.     Two  lines  are  necessary  ;  the  earth  takes  the 
place  of  the  third  line.     For  example,  suppose  we  have : 

Resistance  of  No.  I  and  No.  2,  looped 6550  ohms. 

"   No.  i  and  distant  ground 3625       " 

"  "   No.  2  and  distant  ground 2975       " 

Half  the  sum  of  which  is  6575,  from  which  deduct  loop  resistance 
of  Nos.  i  and  2,  gives  25  ohms  as  resistance  of  ground.  The  resist- 
ance of  a  ground  plate  ought  not  to  exceed  10  ohms. 

349.  Measurement  of  Insulation  Resistance  of  a  Line. 
— In  making  this  test,  the  connections  at  the  home  station  are  the 
same  as  in  the  conductivity  test  (346) ;  the  line  is  open  or  insulated 
at  the  distant  station,  instead  of  being  to  ground.      In  most  cases, 
the  insulation  resistance  will  exceed  the  amount  of  resistance  avail- 
able in  the  E  A  side  of  the  bridge.     In   this  case  the  resistance  in 
A  B  (/>)  must  be  made  greater  than  that  in  B  C  (a).     For  example, 
it  may  be  10  in  B  C  and   100  or   TOGO  in  A  B.      In  this  case,  when 
the  balance  has  been  obtained,  the  amount  unplugged  in  E  A  (d) 
must  be  multiplied  by  10  or  by  100,  as  the  case  may  be,  in  order  to 
obtain  the  correct  resistance.     It  will  be  observed  that  under  these 
conditions,  the  ratio  of  the  resistances  in  the  different  parts  of  the 
bridge  remains  unchanged. 

350.  Location  of  the  Position  of  a  Ground.— When  the 
fault  is  a  dead  ground,  which  is  not  often  the  case,  it  is  a  very  simple 
matter  to  locate  it.     For  example,  if  the  line  were  250  miles  long, 
and   from  previously   recorded   measurements   its  conductivity  was 
known  to  be  3250  ohms,  or   13  ohms  per  mile,  and  the  resistance 
measured  through  the  fault  was  1287  ohms,  then  the  distance  from 
the  testing  station  would  be  1287  -5-  13  =  99  miles. 

351.  Location  of  the  Position  of  an  Escape. — This  is 
one  of  the  most  common  cases  which  arise  in  practice.     If  no  other 
than  the  defective  line  is  available  for  the  measurement,  the  process 
presents  some  difficulties,  for  the  reason  that  the  resistance  of  the 
fault  is  usually  variable.     If  we  have,  for  example  : 

(1)  Resistance  of  line  in  good  order  (from  previous  tests). .   4500  ohms. 

(2)  "  with  distant  end  open  (measured) 35OO      " 

(3)  "  with  distant  end  to  ground  (measured) 2700 

Subtract  (3)  from  (2)  and  also   (3)  from  (i)  ;  multiply  the  two  re- 
mainders together  and  extract  the  square  root  of  the  product,  and 


Varleys  Loop    Test.  203 

finally  subtract  this  result  from  (3).  In  the  above  case,  this  would 
give  the  resistance  of  the  conductor  to  the  fault  as  1500  ohms. 
While  this  method  is  theoretically  accurate,  it  will  not  do  to  depend 
too  much  upon  it  in  practice,  for  the  reasons  given. 

352.  Method  of  Double  Measurement.— Let  two  measure- 
ments be  made,  one  from  each  end,  the  opposite  end  of  the  line 
being  open.     Suppose  the  fault  the  same  as  in  the  last  case.     By 
records  and  measurements  we  have, — 

(1)  Conductivity  resistance  of  wire  when  good. . .  .   4500  ohms. 

(2)  Resistance  measured  from  A  with  B  open 35oo      " 

(3)  "      B  with  A  open 5000 

To  find  the  resistance  from  A  to  the  fault. — Subtract  (3)  from  the 
sum  of  (i)  and  (2),  and  divide  the  remainder  by  2. 

To  find  the  resistance  from  B  to  the  fault. — Subtract  (2)  from  the 
sum  of  (i)  and  (3),  and  divide  the  remainder  by  2. 

The  fault  is  1500  ohms  from  A  and  3000  ohms  from  B,  which 
may  be  reduced  to  miles  as  in  (350). 

353.  The  Loop  Test. — When  a  good  wire  is  available  between 
the  same  points  as  the  defective  wire,  this  method  may  be  made  to 
give  extremely  accurate  results  in   the  hands  of  a  careful  operator. 
The  arrangement   of  the  connections,  the  method   of  making  the 
measurements,  and  the  computation  of  the  result  are  precisely  the 
same  as  in  the  method  described  for  measuring  a  distant  ground  in 
(346).     If  the  resistance  of  the  fault  is  considerable,  care  should 
be  taken  to  employ  sufficient  battery-power  to  get  decided  deflec- 
tions on  the  galvanometer.     The  loop  should  be  made  at  the  nearest 
station  available  beyond  the  fault. 

354.  Varley's  Loop  Test. — The  arrangement  of  connections 
for    this     modification    of 

the  loop  test  is  shown  in 
Fig.  175.  The  defective 
wire  is  looped  with  a  good 
wire,  and  terminal  B  is 

connected   to    a  grounded      ]  ^^Xftn™^ -^  EARTH 

battery.  B  C  and  A  B  are 
the  fixed  resistances  ;  E  A 
is  adjusted  until  equilib- 

rium       is      reached.         The  FlG>  ,7S.     Principle  of  Varley's  Loop  Test. 

actual    connections    are 

shown  in  Fig.  176.     The  calculation  is  made  as  follows  : 

Suppose  a  line  having   a  total  conductivity  resistance  of  4500 


204 


Testing    Telegraphic  Lines. 


A                    B 

j 

D 

g=> 

A' 

i    ^  ^ 

[ 

~£  T            B^ 

I 

E 

EARTH 


ohms  looped  with  another  line  of  the   same  resistance,  we  should 
then  have : 

(1)  Total  resistance  of  loop 9000  ohms. 

(2)  Resistance  in  E  A  to  balance, 6000 

Subtract  (2)  from  (i)  and  divide  remainder  by  2,  gives  number 
of  ohms  between  terminal  E  and  the  fault  (in  this  case  1500),  which 

is  reduced  to  miles  in 
the  usual  way  (350). 

The  defective  wire 
must  always  be  at- 
tached to  terminal  E, 
or  the  needle  cannot 
be  made  to  balance. 
Therefore,  in  case  a 
balance  cannot  be  ob- 
tained, the  obvious 
remedy  is  to  reverse  or 
interchange  the  loop 
connections  with  the 
rheostat. 

355.  To  Locate  a 
Cross.  —  In  case  a 
third  good  wire  is  not  available,  connect  one  of  the  crossed  wires  to 
C  and  the  other  to  E  of  the  bridge.  Make  one  measurement  of  the 
loop  through  the  cross  with  both  lines  open  at  nearest  available  sta- 
tion beyond,  and  another  with  the  same  wires  looped  at  that  station. 
If  the  two  measurements  are  approximately  the  same,  the  number  of 
ohms  in  the  loop  divided  by  2  and  converted  into  miles  will  give  the 
distance  of  the  cross  from  the  testing  station.  If  the  lines  are  of 
different  length,  owing  to  the  routes  being  different,  allowance  must 
be  made  for  the  fact ;  also,  if  the  wires  are  of  different  conductivities 
per  mile. 

356.  When  the  two  measurements  differ  considerably,  showing 
that  the  cross  offers  more  or  less  resistance,  the  above  test  would 
give  a  result  in  excess  of  the  real  distance.  In  such  case  the  follow- 
ing procedure  maybe  adopted.  In  Fig.  177,  suppose  wires  No.  i 
and  No.  2  to  be  crossed  at  X. 

By  measurement  from  A  B  we  get  the  following  results,  for  ex- 
ample : 

(1)  No.  i  from  A  to  C  (with  No.  2  open  at  B  and  D) 3000  ohms. 

(2)  No.  2  and  No.  i  from  A  to  B  through  the  cross  at  X. . .   4650      " 

(3)  No.  2  and  No.  i  from  B  to  C  through  the  cross  at  X. . .   2650      " 


IW*- 


Varley's  Loop  Test. 


Shunts  of  Galvanometers.  205 

Deducting  (3)  from  the  sum  of  (i)  and  (2)  gives  5000,  which 
divided  by  2  gives  2500  ohms,  as  resistance  of  No.  i  wire  from  A  to 
X.  The  distance  on  No.  2  wire  may  be  found,  if  desired,  in  the 
same  way. 


FIG.  177.     Distance  Test  for  Cross. 

357.  When  a  third  wire  in  good  order  is  available,  the  most  con- 
venient as  well  as  the  most  accurate  method  of  locating  a  cross,  is 
to  ground  either  one  or  both  ends  of  one  of  the  crossed  wires  and 
make  the  other  crossed  wire  into  a  loop  with  the  good  wire.     The 
cross  can  then  be  treated  as  a  ground,  and  located  by  one  of  the  loop 
tests  heretofore  given  in  (353)  and  (354). 

358.  To  Locate  a  Bad  Joint  or  Abnormal  Resistance. 
—It  sometimes  happens  that  a  line  gives  a  much  higher  resistance 
than  it  should  do,  according  to  computation  or  by  previous  measure- 
ment.    In  such  cases  a  bad  joint  may  be  suspected.     To  locate  it, 
instruct  a  station  midway  of  the  line  to  put  on  ground.     Take  a 
measurement  through  first  half  of  the  line  and  this  ground,  the  dis- 
tant end  being  open.     This  will  show  whether  the  fault  is  in  the  sec- 
tion measured  or  beyond.     Repeat  the  test  to  another  station  in  the 
middle  of  the  defective  section,  and  so  on  until  it  has  been  fixed 
between  two  sections. 

359.  Measurement   of   very    High    Resistances.— The 
highest  resistance  which  can  be  measured  by  the  Wheatstone  Bridge 
apparatus,  described  in    (344),   is    i   megohm,  or    1,000,000  ohms. 
This  is  a  sufficient  range  to  cover  most  of  the  requirements  ordi- 
narily met  with  in  practical  telegraphy,  but  in  testing  insulators,  or 
the  insulation  resistance  of  very  short  sections  of  out-of-door  line,  it 
is  often  desirable  to  be  able  to  determine  much  higher  resistances. 
The  method  of  proportional  deflections  is  usually  resorted  to  in  such 
cases.     A  galvanometer  having  a  coil  of  a  large  number  of  turns  of 
very  thin  wire  and  a  delicately  suspended  needle  (345)  is  most  suit- 
able for  the  purpose. 

360.  Shunts   of  Galvanometers. — The  galvanometers   for 
this  work  must  be  provided  with  shunts ;  these  are  short  coils  of 
.wire,  arranged  to  be  connected  or  bridged  across  the  terminals  of 
the  galvanometer,  and  are  usually  marked  (to  indicate  their  multi- 
plying power)  i- 10,  i-ioo,  and  in  very  delicate  instruments  usually 
i-iooo  also. 


2O6 


Testing    Telegraphic  Lines. 


FIG.  178.     Shunt  Box  for  Galvanometer, 


The  first  shunt  coil  has  1-9,  the  second  1-99,  and  the  third  1-999 
of  the  resistance  of  the  galvanometer  coil.  They  are  made  of  cop- 
per wire,  that  they  may  be  affected  by  temperature  in  the  same  ratio 
as  the  galvanometer  coils.  Fig.  178  shows  an  arrangement  much 

used,  in  which  either  of 
three  shunts  may  be  thrown 
into  use  at  will  by  changing 
the  peg. 

361.  Measurement  by 
Deflections. — This  meth- 
od is  useful  in  making  com- 
parative tests  of  insulators. 
In  this  case  the  internal  re- 
sistance of  the  testing  bat- 
tery is  inappreciable  in  com- 
parison with  the  resistance  to  be  measured,  and  hence  the  force  of 
the  current  acting  upon  the  needle  may,  without  sensible  error,  be 
regarded  as  proportionate  to  the  e.  m.f.  of  the  battery. 

First,  connect  the  galvanometer  G  in  circuit  with  a  large  known 
resistance  R  (say  10,000  ohms)  and  a  single  cell  E,  whose  e.  m.f.  is 
known,  as,  for  instance,  a  gravity  cell  (9).  If  the  deflection  exceeds 
12°,  reduce  it  to  a  point  below  that  figure  by  the  ^ 

use  of  the  proper  shunts.6  The  arrangement  of 
the  connections  for  performing  this  operation, 
which  is  termed  taking  the  constant  of  the  galva- 
nometer, is  illustrated  in  Fig.  179.  Second,  remove 
the  shunt  and  the  resistance  R,  and  having  re- 
placed the  latter  by  the  unknown  resistance  to  be 
measured,  add  a  sufficient  number  of  cells  of  the 
same  kind  (in  series)  to  produce  a  convenient 
deflection,  not  exceeding  12°,  as  before.  The 
result  is  found  by  simple  rule  of  three,  as  in  the 
example  given  in  the  next  paragraph. 

362.  Measurement  of  Resistance  of  In- 
sulators.— Mount  a  set  of  say  10  insulators, 
I,  Fig.  1 80,  upon  a  suitable  frame  out  of  doors, 
exposed  to  rain  under  the  same  conditions  as  if 
in  actual  service.  Bind  a  line-wire  to  the  whole  series,  and  connect 
this  with  one  terminal  of  the  galvanometer  G,  the  other  terminal  of 

«  The  reason  for  this  procedure  is,  that  above  this  point  the  angles  of  the  deflec- 
tions cease  to  be  proportional  to  the  strength  of  the  currents  producing  them.  (Com- 
pare table  of  tangents,  p.  55.) 


FIG.  179.     Taking 
Constant. 


Measurement  of  Internal  Resistance  of  Battery.   207 

galvanometer  to  zinc  pole  of  battery  E,  and  the  copper  pole  of  bat- 
tery to  ground.  Suppose  that  with  the  particular  galvanometer 
msed,  the  following  results  are  obtained,  the  weather  being  very  wet : 

i  cell  through  10,000  ohms 41 J 

i     "  "         10,000      "     (with  10  shunt) 5° 

Constant  of  galvanometer  (i  cell  through  10,000  ohms). .   50° 

10  cells  through  10  insulators  in  parallel 10° 

Therefore,  if  i  cell  will  give  50°  through  10,000  ohms,  as  per  constant,  10 
cells  will  give  50°  through  100,000  ohms :  and  will  therefore  give  10° 
through  500,000  ohms. 

Hence  the  joint  resistance  of  the   10  insulators  is  500,000  ohms, 
and  their  mean  individual 
resistance  5,000,000  ohms,  ' 

or   5   megohms,   per    insu-  Q  Q  Q  0  Q  Q  0  Q  0  Q 

lator. 

363.  Measurement  of  EG 
the    Internal    Resist-              -          •I1|l|i|i  •!  + /"T\ 

ance  of  a  Battery.-(i)        ( 1 II I  l|l|l|l|l  lp\fj ^ 

It  follows  from  Ohm's  law 

(124)  that  when  the  total     \^><^\ 

resistance    of  any   circuit,  FlG.  l8o.    Test  Of  insulators, 

embracing  that  of  an  in- 
cluded battery  and  galvanometer,  is  doubled,  the  quantity  of  the  cur- 
rent flowing  through  it  is  halved ' ;  and  hence  if  the  indications  of  the 
galvanometer  be  proportional  to  the  strength  of  current,  its  deflection 
will  also  be  halved.  If  a  tangent  galvanometer  (96)  of  known  re- 
sistance is  at  hand,  connect  it  with  a  plugged  rheostat  in  the  circuit 
of  the  battery  to  be  measured.  Reduce  the  sensitiveness  of  the  in- 
strument by  a  shunt  (360),  if  necessary,  to  bring  the  deflection  as 
near  60°  as  possible,  and  note  the  corresponding  tangent  of  the 
deflection  as  given  in  the  table,  p.  55.  Unplug  resistance  until  the 
tangent  of  the  deflection  is  halved,  showing  that  the  total  resistance 
has  been  doubled.  Deduct  the  resistance  of  galvanometer  and  con- 
nections from  the  added  resistance ;  the  remainder  is  the  resistance 
of  the  battery.  Do  not  forget  that  the  shunt,  when  used,  diminishes 
the  resistance  of  the  galvanometer  as  a  part  of  the  measured  circuit. 

364.  (2)    If  the  resistance  of  the   galvanometer   is   unknown,  a 
modification  of  the   Wheatstone   bridge   may  be  used.     Make  the 
connections  as  in  Fig.  181.     Connect  the  terminals  B'  and  E  by  a 
short,  thick  wire.     The   left  (galvanometer)  key  is  permanently  de- 
pressed.    Touch  the  right-hand  key  and  adjust  resistance  A  E  (d) 
until  the  needle  remains  at  rest  (it  will  not  be  at  zero).     It  is  neces- 


208 


Testing   Telegraphic  Lines. 


0 N 


B 


1  \ 

*4 1 j 

j— 1—3 


sary  to  shunt  the  galvanometer  in  this  test.  If  the  resistance  in 
A  B  (a)  is  equal  to  that  in  A  B  (£),  the  amount  unplugged  in  A  E 
is  equal  to  the  resistance  of  the  battery.  In  any  case,  by  proportion, 

A  B  is  to  A  C  as  A  E  is  to  the 
resistance  of  the  battery. 

The  most  accurate  results 
will  be  reached  when  A  B  is  as 
high  and  A  C  is  as  low  as  pos- 

.,  r    i —          sible,  but  not  so  high  as  to 

l\  carry  A  E  beyond  the  range 

of  the  rheostat. 

365.  Measurement  of 
Resistance  of  Galvanom- 
eter. —  If,  in  the  diagram, 
Fig.  1 8 1,  the  battery  and  gal- 
vanometer  are  made  to  change 
FIG.  181.  Resistance  of  Battery.  places,  the  resistance  of  the 

galvanometer  may  be  deter- 
mined in  the  same  way.  Make  B  C  (a)  not  more  than  one-tenth  of  the 
probable  resistance  of  galvanometer,  and  make  A  B  (b)  not  less  than 
ten  times  the  same,  but  not  so  high  as  to  carry  A  E  beyond  the  range 
of  the  rheostat  The  least  possible  value  of  B  C  with  an  ordinary 
bridge  set  would  be  10  ohms.  A  smaller  resistance  might  be  extem- 
porized from  a  piece  of  wire,  if  necessary. 

366.  The  Differential  Galvanometer.— This  instrument  is 
primarily  designed  to  show  the  difference  in  strength  between  two  cur- 
rents.    The  coil  is  wound  throughout  with  two  wires,  equal  in  length, 
resistance,  and  number  of  convolutions,  so  that  the  same  current  in 
each  will  have  a  like  effect  upon  the    needle.     The  two  wires  are 
sometimes  formed  into  a  tape  by  plaiting  together  the  silk  with  which 
they  are    covered.     If,  therefore,  two   equal  currents    traverse    the 
respective  wires  in  opposite  directions,  the  needle  will  not  move.     If 
one  current  be  stronger  than  the  other,  the  needle  will  be  moved  by 
the  stronger  current  with  a  force  due  to  the  difference  in  the  strength 
of  the  two  currents.     This  instrument  was  formerly  much  used  to 
measure  resistances  by  comparing  them  with   standard  resistance 
coils,  but  has  now  been  practically  superseded  by  the  Wheatstone 
bridge  (341). 

367.  Testing  for   Insulation  by  Received   Currents.— 
This  system  of  testing  offers  many  advantages  over  that  hereinbefore 
referred  to  (340)  for  the  daily  examination  of  telegraph  lines.     The 
current  from  a  testing  battery,  of  a  definite  and  approximately  uni- 


Testing  for  Insulation  by  Received  Currents.     209 

form  e.  #/./.,  is  sent  at  a  stated  time  through  the  different  lines,  or 
sections  of  lines,  and  the  volume  of  current,  as  indicated  by  a  tan- 
gent galvanometer  such  as  that  shown  in  Fig.  182,  or  by  an  ammeter 
(369)  at  the  receiving  end,  is  registered.  It  is  evident  that  the 
strength  of  the  received  current  will  be  greater  or  less  as  the  insula- 
tion is  better  or  worse,  and  hence  if  the  e.  m.f.  of  the  battery  be 
constant,  the  volume  of  the  received  currents  as  observed  from  day 


FIG.  182.     Western  Union  Tangent  Galvanometer. 

to  day  will  give  an  accurate  knowledge  of  the  condition  of  the  lines. 
The  normal  resistance  of  each  line  is  known  from  the  stated  con- 
ductivity tests,  and  so  if  the  currents  be  sent  from  a  battery  of  known 
e.  m.  f.  it  is  only  necessary  to  divide  the  latter  amount  by  the  former 
to  know  at  once  the  maximum  current  which  can  possibly  be  received 
through  any  wire.  For  example,  if  a  battery  of  50  cells  be  used  on 
a  circuit  of  2500  ohms,  then 

50  volts  -f-  2500  ohms  —  0.02  ampere. 

This  may  be  regarded  as  the  standard  current  of  that  circuit,  and 
the  greater  the  leakage  the  greater  will  be  the  diminution  of  the  cur- 
rent below  that  standard.  Tables  may  be  made  for  convenient  refer- 
ence showing  the  normal  current  of  each  line.  Special  faults  are  of 


2io  Testing   Telegraphic  Lines. 

course  investigated  by  the  bridge  apparatus  (341)  when  their  presence 
has  been  revealed  by  the  procedure  above  described. 

368.  Use   of  the    Voltmeter   and   Ammeter  in   Tele- 
graphic Testing. — Since  the  general  introduction  of  electricity 
in  lighting  and  power  service,  a  new  class  of  instruments  for  the 
measurement  respectively  of  potential  and  current,  known  as  volt- 
meters and  ammeters,  have  been  brought  to  great  perfection,  and  are 
now  frequently  employed  with  advantage  in  telegraphic  work.     Much 
time  is  saved  in  making  readings  and  computations,  as  a  simple  in- 
spection of  the  indication  of  the  pointer  on  the  scale  at  once  gives 
the  result  in  volts  or  amperes.     The  pointer  comes  to  rest  promptly, 
so  that  a  reading  dan  be  made  almost  instantaneously. 

369.  The  Weston   Ammeter  and  Voltmeter. — Fig.  183 
shows  Weston's  portable  type  of  direct-reading  mil-ammeter,  about 

one-fourth  its  actual  size. 
It  comprises  a  permanent 
magnet,  having  a  hollow 
rectangular  coil  of  alumin- 
ium wire  suspended  within 
its  field  upon  jeweled  piv- 
ots, to  which  coil  the  pointer 
is  attached.  Fig.  184  is  a 
full-sized  view  of  the  work- 
ing parts  of  the  instrument. 
One  of  the  most  useful  types 
for  telegraphic  work  has  a 

FIG.  ,83.    Weston's  Mil-ammeter.  scale  reading  to  i  ampere, 

with  subdivisions  of  10  mil- 
amperes,  which  may  be  read  by  inspection  to  a  single  mil-ampere.7 
Another  type,  which  is  adapted  to  perform  all  the  measurements 
ordinarily  required  in  a  large  telegraph  station,  is  provided  with 
several  scales ;  one  of  a  single  volt,  which  may  be  read  to  .001  volt, 
for  determining  the  potential  of  a  single  cell ;  another  of  o  to  500 
volts  (which  can  be  read  to  single  volts  or  half  volts),  for  taking  the 
potential  of  a  large  number  of  cells  when  connected  in  series  in  a 
single  battery  ;  another  of  i  ampere  (which  can  be  read  to  mil- 
amperes)  for  determining  the  strength  of  currents.  Some  are  made 

7  The  construction  of  the  voltmeter  and  ammeter  are  simLar,  the  difference  being 
in  the  length  and  thickness  of  the  wire  in  the  deflecting  coil,  which  is  made  long,  thin, 
and  of  great  resistance  in  the  voltmeter,  and  comparatively  short  and  thick  and  of 
small  resistance  in  the  ammeter.  Two  or  more  coils  of  different  lengths  may  be  fitted 
to  the  same  instrument,  as  in  a  galvanometer,  giving  different  grades  of  sensibility. 


The  Weston  Ammeter  and  Voltmeter.        211 

with  a  coil  of  precisely  100  ohms  resistance,  giving  a  full  scale 
deflection  with  i  volt.  Such  an  instrument  is  very  convenient  for 
measuring  line  resistances.  For  example,  with  100  volts  the  resist- 
ance in  circuit  required  to  bring  the  pointer  to  the  upper  division  of 
the  scale  would  be  10,000  ohms,  and  hence  by  pointing  off  two 
decimal  places  any  resistance  in  ohms  in  the  circuit  may  be  deter- 
mined by  direct  reading  from  the  scale,  in  the  same  manner  as  volts. 


FIG.  184.     Mechanism  of  Weston's  Direct-Reading  Instrument 

The  Weston  instruments  are  particularly  well  adapted  for  all  cur- 
rent measurements  usually  performed  with  a  tangent  galvanometer 
(102).  They  are  not  only,  for  most  purposes,  more  accurate,  but 
are  far  more  convenient,  as  they  may  be  placed  in  any  position,  and 
are  in  no  wise  affected  by  the  neighborhood  of  masses  of  iron  or  of 
foreign  electric  currents.  No  time  need  be  lost  in  leveling,  adjust- 
ing, or  waiting  for  the  needle  to  settle,  while  the  convenience  of 
being  able  to  read  off  the  results  directly  without  calculation  is  very 
great. 

Another  and  a  very  important  advantage  is,  that  the  tests  may  be 
made  with  the  same  current  which  is  employed  in  the  ordinary 
operation  of  the  circuit  Tests  for  resistance,  especially,  not  unfre- 
quently  give  very  fallacious  results,  when  made,  as  is  often  the  case, 


212 


Testing   Telegraphic  Lines. 


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214  Testing   Telegraphic  Lines. 

with  a  current  of  much  lower  potential  than  the  actual  working 
current. 

370.  Recording  Tests  of  Conductivity  and  Insulation.— 
The  forms  of  returns  for  line  tests  adopted  by  the  Western  Union 
Telegraph  Company  are  given  on  pp.  212,  213.  When  the  tangent  in- 
strument is  used,  the  constant  (361)  is  written  in  the  upper  right-hand 
corner  of  the  sheet.  One  horizontal  line  is  appropriated  to  each 
separate  wire  tested.  The  headings  sufficiently  explain  entries  to  be 
made  in  the  several  columns.  When  the  tests  are  made  by  the  bridge 
apparatus,  the  results  are  entered  directly  in  the  resistance  columns, 
but  if  with  the  tangent  instrument,  these  are  computed  and  filled  up 
at  the  electrician's  office  in  New  York.  The  same  observations  ap- 
ply to  the  insulation  form.  The  record  of  the  wet  and  dry  bulb 
thermometer  is  important,  as  it  enables  the  percentage  of  moisture 
in  the  air  to  be  determined  and  its  effect  upon  the  different  kinds 
of  insulation  to  be  compared  and  studied. 

By  inspecting  and  comparing  these  sheets,  as  returned  from  the 
various  testing  offices,  the  electrician's  department  is  kept  fully 
informed  of  the  electrical  condition  of  the  lines  in  all  parts  of  the 
country.  The  system  of  stated  reports  was  instituted  by  Lefferts, 
of  the  American  Telegraph  Company,  in  i863,8  and  has  resulted  in 
a  vast  improvement  in  the  efficiency  of  the  service. 

8  LEFFERTS  (MARSHALL),  born  January  15,  1821,  in  Bedford,  now  part  of  Brook- 
lyn, N.  Y.  In  early  life  he  was  a  civil  engineer  and  was  employed  in  laying  out  the 
city  of  Brooklyn.  Subsequently  he  became  a  successful  merchant  in  New  York  City, 
and  a  prominent  militia  officer.  In  1849  his  marked  scientific  tastes  led  him  to  be- 
come interested  in  telegraphy.  Entering  into  the  new  enterprise  with  the  energy  and 
zeal  which  were  among  his  most  notable  characteristics,  he  organized  and  became  the 
president  and  manager  of  a  range  of  lines  operating  the  Bain  electro-chemical  sys- 
tem, extending  from  New  York  to  Boston  and  Buffalo.  Legal  complications  in  con- 
nection with  patents  eventually  led  to  a  consolidation  of  these  lines  with  those  con- 
trolled by  the  Morse  patentees,  in  consequence  of  which  he  resumed  for  a  time  his 
manufacturing  and  mercantile  business.  In  1860  he  was  appointed  engineer  and  exec- 
utive manager  of  the  American  Telegraph  Company,  which  under  his  administra- 
tion became  one  of  the  most  popular  and  successful  telegraph  organizations  that  ever 
existed  on  this  continent.  He  retained  this  position  until  the  consolidation  of  the 
American  with  the  Western  Union  Telegraph  Company  in  1866,  and  subsequently 
occupied  a  responsible  post  in  the  united  service  until  1871.  At  this  date  he  was 
elected  president  of  the  Gold  and  Stock  Telegraph  Company  of  New  York,  which  po- 
sition he  held  until  his  death.  He  possessed  a  most  unusual  organizing  and  executive 
ability,  and  while  a  strict  disciplinarian,  it  afforded  him  genuine  pleasure  to  discover 
and  to  reward  meritorious  service,  even  in  the  humblest  capacity.  His  uniformly  just 
and  considerate  treatment  of  his  employees,  no  less  than  his  genial  and  kindly  spirit, 
insured  the  most  loyal,  enthusiastic,  and  diligent  service  from  all.  By  a  liberal  system 
of  advancement  to  the  intelligent,  the  skillful,  and  the  deserving,  the  standard  of 
character  and  acquirements  among  the  employees  of  the  American  Company  was 
elevated  to  an  extent  to  which  later  times  have  afforded  few  parallels.  As  engineer  of 


Recording  7 ^esis  of  Conductivity  and  Insula tiou.    215 

this  extensive  organization,  he  labored  unceasingly  to  place  its  service  upon  a  perma- 
nent foundation  befitting  its  importance  and  its  high  mission.  He  was  the  first  to 
appreciate  the  importance  of  testing  lines  and  apparatus,  and  it  is  to  the  standard  ot 
excellence  which  he  established  that  the  commencement  of  the  era  of  scientific  teleg- 
raphy in  America  may  be  traced.  Assuming  in  1861  the  administrative  management 
of  a  heterogeneous  assemblage  of  poorly  built  and  ill-arranged  telegraphs,  equipped 
with  a  miscellaneous  collection  of  apparatus  of  antiquated  and  unserviceable  types,  he 
five  years  later  turned  over  to  the  Western  Union  Company  30,000  miles  of  wire, 
constituting  perhaps  the  most  complete,  thoroughly  organized,  and  efficient  tele- 
graphic system  in  the  world.  The  influence  of  the  reforms  and  improvements  which 
were  instituted  during  his  administration  will  continue  to  be  felt  in  the  American 
telegraph  service  for  all  future  time.  He  died  suddenly,  July  3,  1876,  while  on  his 
way,  as  commander  of  a  military  organization,  to  participate  in  the  celebration  of  the 
centennial  anniversary  of  the  Declaration  of  American  Independence,  in  Philadelphia. 


CHAPTER    X. 

HINTS     TO     LEARNERS. 

371.  Formation  of  the  Telegraphic  Code. — The  code  of 
alphabetical  and  numerical  signals  employed  in  telegraphy,  as  devised 
by  Vail  in  1837,!  is  made  up  of  various  combinations  of  a  small 
number  of  elements.  In  the  so-called  "  Morse  "  code,  as  used  in 
America,  there  are  seven  of  these  elements,  viz. : 

(i)  The  dot;  (2)  theitasA;  (3)  \hzlongdash;  (4)  the  ordinary 
space;  (5)  the  letter-space;  (6)  the  word-space;  and  (7)  the  sentence- 
space.  It  is  important  to  remember  that  the  value  of  the  spaces  in 
the  code  is  as  great  as  that  of  the  dots  and  dashes.  A  common 
misconception  exists  in  the  minds  of  students  that  the  telegraphic 
code  consists  exclusively  of  dots  and  dashes.  The  foundation  of 
perfect  telegraphic  manipulation  lies  in  the  ability,  which  can  only 
be  acquired  by  careful  observation  and  training,  to  accurately  divide 
and  subdivide  time  into  intervals  which  are  multiples  of  an  arbitrary 
unit. 

1  VAIL  (ALFRED),  born  at  Speedwell,  near  Morristown,  N.  J.,  September  25,  1807. 
In  early  life  he  became  an  apprentice  in  his  father's  Speedwell  iron- works.  After  attain- 
ing his  majority,  he  pursued  a  course  of  study  and  graduated  at  the  University  of  the 
City  of  New  York  with  the  intention  of  entering  the  ministry,  but  in  September,  1837, 
chancing  to  witness  one  of  the  early  experiments  of  Morse  with  his  crude  telegraphic 
apparatus,  his  mind,  naturally  of  a  strongly  scientific  cast,  was  instantly  fired  with 
enthusiasm  at  the  future  possibilities  of  this  marvelous  invention.  He  became  wholly 
absorbed  in  the  enterprise,  and  persuaded  his  father,  Stephen  Vail,  to  furnish  the 
means  required  to  perfect,  develop,  and  introduce  the  electric  telegraph.  Among  the 
improvements  in  the  apparatus  and  methods  originated  by  himself,  of  the  utmost  prac- 
tical value,  were  the  register  (269),  which  is  to-day  but  little  changed  from  the  form 
he  gave  it  in  1844,  and  the  "Morse"  alphabetical  code  (372),  now  in  universal  use  in 
America.  (See  American  Inventors  of  the  Telegraph,  Century  Magazine,  xxxv.  924, 
April,  1888.)  The  efforts  of  Vail  in  overcoming  the  numerous  practical  difficulties 
that  beset  the  work  of  installing  the  pioneer  telegraph  line  between  Washington  and 
Baltimore  in  1844,  were  indefatigable,  and  it  is  to  his  genius,  patience,  and  untiring 
diligence  that  the  ultimate  success  of  the  enterprise  was  in  no  small  measure  due. 
The  last  ten  years  of  his  life  were  passed  by  him  in  comparative  retirement,  engaged 
in  his  favorite  pursuits  of  science  and  literature.  He  died  at  Morristown,  January  18, 
1859- 


The  American  Morse  Code. 


217 


372.  The  American  Morse  Code.— The  complete  code  as 
now  used  in  the  United  States  and  Canada,  comprising  letters, 
numerals,  punctuation,  and  other  signs  more  or  less  used,  is  given 
below : 

I.    ALPHABET   AND    NUMERALS. 


A 

B 
C 
D 
E 
F 
G 
H 
I 

J 

K 

L 

M 


N 
O 
P 

Q 

R 

S 
T 

U 
V 

w 

X 
Y 
Z 

& 


nrm 


The  arbitrary  unit  of  time  in  this  code,  which,  when  written  down, 
becomes  a  unit  of  length,  is  technically  termed  the  dot ;  an  unfortu- 
nate name  for  this  element,  inasmuch  as  it  conveys  the  idea  of  an 
inappreciable  lapse  of  time,  or  of  the  transmission  of  a  current  of 
infinitely  short  duration.  On  the  contrary,  an  appreciable  time  is 
required  for  the  production  of  signals  by  electricity  (315);  in  the 
magnetization  of  electro-magnets  (195),  and  in  the  movement  of 
clock-work.  The  formation  of  a  dot,  therefore,  necessarily  involves 
time.  Assuming,  therefore,  that 

(1)  The  dot  is  the  unit  of  time, 

(2)  The  dash  is  equal  to  2  dots  ; 


218 


Hints  to  Learners. 
II.    PUNCTUATION,    ETC. 


Comma,                                    , 

• 

• 

• 

• 

• 

• 

Semicolon,                                ; 

• 

• 

• 

• 

• 

Colon,                                        ; 

• 

• 

• 

• 

• 

• 

• 

Colon  Dash,                            :  — 

• 

• 

• 

• 

• 

• 

• 

• 

i    • 

Period,' 

• 

• 

• 

• 

• 

• 

• 

• 

Interrogation,                           ? 

• 

• 

• 

• 

• 

• 

• 

Exclamation,                             J 

• 

• 

• 

• 

• 

• 

• 

Dash, 

• 

• 

• 

• 

• 

• 

• 

• 

• 

Hyphen, 

• 

• 

• 

. 

- 

• 

• 

i    • 

Pounds,2                                   £ 

l 

I 

Shillings,2                                  / 

• 

• 

• 

• 

• 

• 

Dollars,2                                    $ 

• 

• 

• 

• 

• 

• 

• 

1 

Capitalized  Letter,3 

• 

• 

• 

• 

• 

• 

• 

• 

Colon-Quotation,                     :  " 

• 

• 

. 

• 

• 

• 

• 

• 

1        • 

Decimal  Point, 

• 

• 

• 

• 

• 

• 

• 

Paragraph,                                 If 

• 

• 

• 

• 

• 

• 

• 

• 

Parenthesis  3                                 (   } 

M 

• 

J.   ell  C  1  J  LllCoiOy                                                                 1        i 

Underline,8 

• 

• 

• 

• 

• 

• 

• 

• 

• 

1 

Quotation,3                                 ** 

• 

• 

• 

• 

• 

• 

• 

• 

Quotation  within  Quotation,8  u  * 

« 

• 

• 

• 

• 

• 

" 

• 

• 

(3)  The  long  dash  is  equal  to  4  dots  ; 

(4)  The  ordinary  space  between  the  elements  of  a  letter  is  equal  to  I  dot ; 

(5)  The  letter-space  is  equal  to  2  dots  ; 

(6)  The  word-space  is  equal  to  3  dots  ; 

(7)  The  sentence-space  is  equal  to  6  dots. 

3  To  be  used  before  the  characters  to  which  it  refers. 

3  To  be  used  before  and  after  the  words  to  which  it  refers. 


Handling  the  Key,  219 

The  old  rule  in  transmission  was  to  make  the  dash  equal  to  3,  and 
the  long  dash  to  6,  dots.  When  the  receiving  was  largely  done  by 
recording  instruments  this  was  a  most  necessary  requirement,  for  a 
dot,  and  a  dash  equal  to  only  2  dots,  might  easily  be  mistaken  for 
each  other  in  reading  by  sight,  but  now  that  receiving  by  sound  has 
become  practically  universal,  this  objection  has  lost  its  force,  and  by 
shortening  the  dashes  a  material  gain  in  rapidity  of  transmission  is 
effected  without  any  corresponding  disadvantage. 

373.  Learning  the  Code. — The  student  should  first  thoroughly 
commit  to  memory  the  groups  of  signs  representing  the  letters  of 
the  alphabet,  the  numerals,  and  the  principal  punctuation  points,  viz., 
the/mW,  the  comma,  and  the  point  of  interrogation.     The  remaining 
characters  can  be  learned  afterwards,  as  they  will  be  little  needed  by 
the  beginner. 

374.  Handling   the    Key. — The   most   approved   manner   of 
grasping  the  key,  and  one  which  has  been  employed  by  some  of  the 
most  successful,  experienced  and  rapid  American  operators,  is  shown 


FIG.  185. 

in  Fig.  185.  Curve  the  fore-finger,  but  do  not  hold  it  rigid.  Let  the 
thumb  press  slightly  in  an  upward  direction  against  the  knob.  Keep 
the  wrist  well  above  the  table.  No  better  general1  direction  can  be 
given  than  that  the  key  should  be  grasped,  held,  and  controlled  with 
the  same  flexible  but  perfectly  controlled  muscular  action  of  the  fin- 
gers, wrist,  and  fore-arm  with  which  the  skilled  penman  holds  his  pen. 
Carefully  avoid  tapping  upon  the  knob  of  the  key  ;  the  raising  spring 
should  assist  the  upward  motion  of  the  key,  but  should  never  be 
permitted  to  control  it. 

By  constant  drill,  as  hereinafter  directed,  the  habit  of  making  dots 
with  regularity,  uniformity,  and  precision  must  first  be  acquired ; 
then  dashes,  and  lastly  in  order,  group  of  clots  and  dashes,  letters 
and  words.  If  possible  for  the  student  to  obtain  a  register  (269), 
he  should  by  all  means  employ  it  in  his  practice,  for  he  will  then  be 
more  easily  enabled  to  observe  and  correct  the  faults  in  his  own 


22O  Hints  to  Learners. 

manipulation.  In  commencing,  the  habit  should  at  once  be  acquired 
of  making  the  dots  like  short,  firm  dashes.  The  student  should 
learn  to  form  the  conventional  characters  accurately  and  perfectly  ; 
speed  will  come  in  good  time,  but  only  as  the  result  of  constant  and 
persistent  practice,  accompanied  by  a  determination  to  excel. 

375.  Elementary  Principles  of  the  Code.—  As  a  basis  for 
practice,  the  code  may  be  regarded  as  comprising  six  elementary 
principles,  viz.  : 

First  principle.      Associated  dots. 

I  S  H  P  6 

Second  principle.      Associated  dashes. 


Third  principle.      Isolated  dots. 

E 

Fourth  principle.      Isolated  dashes. 

L  or  cipher. 

Fifth  principle.      Dot  followed  by  dash. 

A 

Sixth  principle.      Dash  followed  by  dot. 

N 

376.    Preliminary  Practice  with   the   Key.  —  The   student 
should  first  practice  upon  the  above  elementary  principles. 

(1)  Make   dots   with  the   key  at  uniform  and   regular  intervals, 
until  they  can  be  produced  with  the  precision  of  a  machine,  and  of 
definite  and  uniform  dimensions.     The  student  will  find  this  more 
easy,  if  at  first  he  times  himself  by  the  beats  of  a  watch  or  a  small 
clock. 

(2)  Next,  make  dashes,  first  at  the  rate  of  about  one  per  second, 
which  speed  may  be  increased  by  degrees,  as  skill  is  acquired  by 
practice,  to  three  per  second.     Make  the  space  interval  between  suc- 
cessive dashes  as  short  as  possible.     If  the  upward  movement  which 
forms  the  space  be  made  full,  it  cannot  be  made  too  quickly. 

(3)  The  third  principle  occurs  but  once,  and  needs  no  specific 
directions. 

(4)  This  principle  will  be  found  somewhat  more  difficult  to  exe- 
cute.    The  usual  tendency  is  to  make  T  too  long,  and  L  too  short. 
Theoretically,  the  cipher  is  one-half  longer  than  L,  but  in  fact  it  is 
always  made  the  same,  as  the  practice  has  been  found  to  occasion 


Preliminary  Practice  with  the  Key.          221 

no  inconvenience.     Occurring  alone,  or  among  other  letters,  it  is 
translated  as  L,  but  when  found  among  figures  is  read  as  o. 

(5)  The  fifth  principle  forms  the  letter  A.     The  usual  tendency  is 
to  separate  the  two  elements  too  much. 

(6)  The  dash  followed  by  a  dot  (N)  is  usually  found  to  be  some- 
what difficult.     Time  the  movement  by  pronouncing  the  word  ninety, 
sounding  the  first  syllable  fully.     Guard  especially  against  the  usual 
tendency  to  separate  the  elements  by  too  great  a  space. 

377.  Exercises  upon  Code  Characters. — Having  become 
thoroughly  familiar  with  the  principles,  the  following  exercises  may 
with  advantage  be  taken  up  in  order : 

(1)  E  I  S  H  P  6 

These  should  be  practiced  repeatedly  until  the  correct  number  of 
dots  in  each  character  can  be  certainly  made  at  every  trial.  A  habit 
once  formed  of  making  the  wrong  number,  usually  one  or  two  too 
many  in  the  case  of  H,  P,  and  6,  is  almost  impossible  to  eradicate. 
Guard  especially  against  the  objectionable  habit  of  shortening  or 
dipping  the  final  dot,  a  vice  which  leads  to  innumerable  and  vexa- 
tious errors  and  misreading  of  signals. 

(2)  T  M  5  1[ 

The  faults  to  be  particularly  guarded  against  in  this  exercise  are 
shortening  or  elongating  the  terminal  dash,  and  separating  the  suc- 
cessive dashes  by  too  great  a  space  interval. 

(3)  _A_  _U_  _V_  _4_ 

The  usual  tendency  to  allow  too  much  space  between  the  dot  and 
dash  in  the  above  letters  may  be  overcome  by  forming  them  as  by 
an  elongation  of  the  final  dot  in  I,  S,  H,  and  P. 

(4)  I  A  S  U  H  V 

Practice  these  characters  in  pairs,  that  the  distinction  between 
them  may  be  more  firmly  impressed  upon  the  mind. 

(5)  N  D  B  8 

The  student  who  has  mastered  the  sixth  principle  will  find  no 
difficulty  with  the  above  characters. 

(6)  A  F  X  ,  W  i 


222  Hints  to  Learners. 

(7)  U  Q  2  Period  3 

These  are  similar  to  preceding  exercises  and  present  no  new 
difficulties. 

(8)  K  J  9  ? 

G  7  Exc. 

J  and  K  are  usually  considered  the  most  difficult  letters  in  the 
code.  Avoid  the  tendency  to  separate  J  by  a  space  into  double  N, 
and  be  careful  that  the  dashes  are  of  equal  length.  The  numerals  7 
and  9  require  some  care  to  ensure  correct  spacing. 

(9)  O  R  &  C  Z  Y 

These  are  termed  the  spaced  letters,  and  the  utmost  care  and  dili- 
gent practice  are  necessary  in  order  to  form  them  accurately.  The 
ability  to  transmit  the  spaced  letters  with  absolute  correctness  is  the  test 
of  a  strictly  first-class  sender.  The  space  should  be  just  enough  in 
excess  of  that  ordinarily  used  between  the  elements  of  a  letter  to 
enable  the  letters  intended  to  be  made  to  be  distinguished  with  cer- 
tainty from  I,  S,  and  H.  The  most  usual  tendency  is  to  make  the 
space  too  great,  even  in  some  cases  as  great  as  the  space  between 
letters.  This  is  a  most  fruitful  source  of  misapprehension  and  error, 
and  too  much  pains  cannot  be  taken  to  acquire  and  maintain  cor- 
rect habits  in  this  particular. 

In  transmitting  words  containing  groups  of  two  or  more  spaced 
letters,  careful  operators  are  accustomed  to  slightly  increase  the 
spacing  between  the  successive  letters  of  the  group. 

Practice  in  transmission  from  miscellaneous  manuscript  is  strongly 
recommended.  The  ability  to  read  all  kinds  of  copy ;  good,  bad, 
and  indifferent,  correctly  at  sight,  is  a  most  valuable  one,  and  is  not 
difficult  to  acquire  by  attention  and  experience. 

If  the  principles  here  laid  down  be  firmly  adhered  to,  the  learner 
will  find  much  reason  for  encouragement,  not  only  at  the  rapidity 
with  which  he  will  master  what  at  first  sight  appears  to  be  a  very 
difficult  undertaking,  but  at  the  extreme  accuracy  with  which  he 
will  be  able  to  manipulate  his  instrument  after  a  fair  amount  of 
practice.  He  must  also  carefully  bear  in  mind  that  one  of  the  most 
universal  faults  among  those  attempting  to  learn  the  telegraphic  art, 
is  that  of  going  over  a  great  deal  of  ground  and  learning  nothing 
thoroughly. 


Reading  by  Sound.  223 

378.  Reading  by  Sound. — This  art  can  only  be  acquired  by 
constant  and  persevering  practice,  keeping  in  mind  the  principles 
above  given.     The  lever  of  the  telegraphic  sounder  makes  a  sound 
at  each  movement,  the  downward  motion  producing  the  heavier  one. 
The  down-stroke  indicates  the  commencement  of  a  dot  or  a  dash  and 
the  up-stroke  its  termination.     A  dot  makes  as  much  sound  as  a 
dash  ;  the   only  difference  is  in  the  length  of  time  or  interval  which 
elapses  between  the  two  successive  sounds.     Thus,  if  the  recoil  or 
up-stroke  were  absent,  it  would  be  impossible  to  distinguish  E,  T, 
and  L  from  each  other. 

379.  In  learning  to  read  by  sound  it  is  advisable  for  two  persons 
to  practice  together,  taking  turns  at  reading  and  writing,  and  each 
correcting  the  faults  of  the  other.     The  sounds  of  the  code  charac- 
ters must  first  be  learned  separately,  and  then  short  words  chosen, 
which  must  be  written  very  slowly  and  distinctly  and  well  spaced, 
the  speed  of  manipulation  being  gradually  increased  as  the  student 
becomes   more   proficient  in  reading.     After  becoming  sufficiently 
well  versed  in  the  art  to  read  at  the  rate  of  twenty-five  or  thirty  words 
per  minute,  further  practice  may  best  be  had  in  copying  with  a. pen 
and  ink  (not  with  a  pencil)  from  a  sounder  connected  with  a  line 
employed  in  transmitting  ordinary  commercial  and  railway  messages, 
in  order  that  the  student  may  familiarize  himself  with  the  technical 
usages  of  the  lines,  and   the  minute   details  of  actual  telegraphic 
business.4 

380.  A  Parting  "Word. — In  conclusion,  the  student  is  warned 
against  falling  into  the  common  error,  which  is  not  confined  to  teleg- 
raphy, of  expecting  great  results  from  little  labor.     To  become  an 
expert  sending  and  receiving  operator  requires  a  vast  amount  of 
time  and  patience,  and  the  most  unwearied  application.     Remember 
that  whatever  is  worth  doing  at  all,  is  worth  doing  well.     It  is  seldom 
that  a  thoroughly  competent  operator  cannot  obtain  immediate  and 
remunerative  employment,  and  it  is  probable  that  such  will  continue 
to  be  the  case,  however  crowded  the  lower  walks  of  the  avocation 
may  hereafter  become. 

4  Full  explanations  respecting  the  methods,  regulations,  and  forms  usually  employed 
in  the  commercial,  railway,  and  express  service,  in  the  forwarding  and  reception  of 
messages,  train  orders,  reports,  etc.,  and  much  other  miscellaneous  information  of  like 
character  useful  to  the  student  of  telegraphy,  may  be  found  in  the  later  editions  of 
Abernethy's  Modern  Service  of  Commercial  and  Railway  Telegraphy.  A  little  work 
by  T.  J.  Smith,  on  The  Philosophy  and  Practice  of  Morse  Telegraphy^  may  also  be 
consulted  with  advantage. 


INDEX 


ABERNETHY'S  Commercial  and  Railway  Te-  \ 
legraphy  referred  to,  223. 

Absolute  system  of  measurement,  37;  con- 
crete example  of,  37. 

Accumulator  or  storage  battery,  how  shown 
in  diagram,  104. 

Accumulation,  electrostatic,  upon  insulated 
conductor,  177. 

Adjustment  of  key,  140 ;  of  quadruplex  ap- 
paratus, 188  ;  of  register,  148 ;  of  sounder, 
142. 

Air,  non-conducting  properties  of,  57. 

Alloys  of  metals,  inferior  conducting  power 
of,  57. 

Alternating  current,  167 ;  rectification  of, 
167. 

Amalgamation  of  zinc,  21. 

American  modification  of  closed-circuit  sys- 
tem, 108. 

American  lines,  defective  insulation  of,  118. 

American  electrical  society,  journal  of,  refer- 
ence to,  187. 

American  institute  of  electrical  engineers, 
extract  from  transactions  of,  2. 

American  standard  wire-gauge,  95. 

Ammeter  or  amperemeter,  the,  44,  61 ;  use  of 
in  telegraphic  testing,  210 ;  Weston's  port- 
able, 211 ;  advantages  of  for  testing,  211. 

Ammeter,  Weston's  combined  voltmeter  and, 
for  telegraphic  testing,  210. 

Ampere,  Andre  Marie,  biographical  notice 
of,  60. 

Ampere,  the  unit  of  current,  definition  of, 
60  ;  value  of,  60  ;  determination  of,  60. 

Ampere-turns,  85 ;  magnetization  propor- 
tional to,  87. 

Amperemeter  or  ammeter,  the,  61. 

Anderson's  machine  for  winding  helices  of 
electro-magnets,  93. 

Anthony,  Wm.  A.,  Review  of  Modern  Elec- 
trical Theories,,  reference  to,  2. 

Apparatus,  electric,  drawings  of,  103 ;  tele- 
graphic, conventional  representations  of, 
103,  104. 

Apparent  resistance  of  line,  128 ;  table  of,  129. 

Armature  of  magnet,  26  ;  of  electro-magnet, 
91  ;  polarized,  100. 

Armature  time  of  telegraph  magnet  deter- 
mined, 99. 

Artificial  line  of  multiple  telegraph,  the,  174. 

Artificial  magnet  defined,  24. 

Astatic  system  of  needles,  198 ;  gal  manom- 
eter. 200. 

Attraction  and  repulsion,  magnetic,  28 ;  mu- 
tual, between  electric  conductors,  35. 

Attraction,  magnetic,  ratio  of  to  distance,  89. 

Authors  referred  to : 
Abernethy,  J.  P.,  223. 
Anthony,  William  A.,  2. 
Avery,  Elroy  M.,  70. 
Becker,  C.,  62. 


Benoit,  Rene,  57.     • 

Bidwell,  Shelford,  26. 

Blavier,  E.  E.,  17,  128. 

Bonsanquet,  R.  H.  M.,  81. 

Bottone,  Selino  R.,  46. 

Bradley,  Leverett,  17,  76. 

Brooks,  David,  119,  120. 

Cavendish,  Henry,  a. 

Chaperon,  G.,  23. 

Christie,  Samuel  Hunter,  195. 

Clark,  Latimer,  58,  76,  125,  198. 

Clerk-Maxwell,  James,  2. 

Cooke,  Josiah  P.,  6. 

Daniell,  Alfred.  2,  38. 

Davis,  Daniel,  jr.,  89. 

Dean,  G.  W  ,  99. 

Everett,  J.  D.,  38. 

Swing",  J.  A.,  98. 

Faraday,  Michael,  2,  3,  29,  38,  73,  M. 

Farmer,  Moses  G.,  62,  119,  128,  136. 

Franklin,  Benjamin,  2. 

French,  E.  L.,  87. 

Gavarret,  J.,  128. 

Gee,  W.  W.  Haldane,  62. 

Gray,  Andrew,  40. 

Grove,  Sir  William,  38. 

Healy,  Clarence  L.,  187. 

Helmholtz,  Herman  L.  F.,  38. 

Henning,  Thomas,  187. 

Henry,  Joseph,  2,  80. 

Hering,  Carl,  82. 

Hill,  Edward  A.,  17. 

Hughes,  David  £.,24. 

Jamieson,  Andrew,  73. 

Jenkin,  Fleeming,  17,  18,  62,  19!. 

Johnson,  A.  J.,  20. 

Jones,  Francis  W.,  187. 

Kapp,  Gisbert,  24,  83. 

Kempe,  A.  BM  128. 

Kempe.  H.  R.,  128,  198. 

Kennelly.  A.  E.,  85. 

Kohlrausch,  F.,  62. 

Lalande,  de,  F.,  23. 

Lockwood,  Thomas  D.,  23,  34. 

Lodge,  Oliver  J.,  2,  88. 

Maver,  William,  Jr.,  185,  187. 

Mayer,  Alfred  M.,  24. 

Mayer,  Julius  R.,  38. 

Morse,  Samuel  F.  B.,  128. 

Munroe,  John,  73. 

Niaudet,  Alfred,  62. 

Nipher,  Francis  E.,  40. 

Nystrom,  John  W.,  28. 

Plum,  H.  W..  187. 

Pope,  Franklin  L  ,  17,  76,  80,  187. 

Preece,  William  ll,  79. 

Prescott,  George  B.,  62. 

Prescott,  George  B.,  Jr.,  74,  94,  ua. 

Rowland,  H.  A.,  81,  88. 

Sabine,  Robert,  83. 

Schott,  C.  A.,  40. 

225 


226 


Index. 


Shaffuer,  Tal  P.,  62. 
Smith,  T.  Jarrard,  223. 
Sprague,  John  T.,  38,  57,  62,  74. 
Stewart,  Balfour,  38,  62. 
Sturgeon,  William,  80. 
Thompson,  Silvanus  P.,  31,  86,  87,  93,  198. 
Thomson,  Sir  William,  2,  73,  88,  93. 
Trowbridge,  John,  40,  85. 
Tyndall,  John,  38. 
Varley,  Cromwell  F.,  131,  135. 
Webb,  F.  C.,  175. 
Wheatstone,  Sir  Charles,  195. 
Wilkinson,  H.  D.,  85. 
Youmans,  Edward  L.,  38. 
Automatic  repeaters,   management  of,  166 ; 
Milliken's,  165. 

BAD  JOINT  ON  LINE,  m^hod  of  locating,  205. 

Balancing  of  resistance  in  multiple  telegraph, 
174. 

Bar  magnet,  24. 

Batteries,  composed  of  number  of  cells,  3. 

Battery,  method  of  determining  cost  of  main- 
tenance of,  75  ;  position  of  in  closed-cir- 
cuit system  of  telegraphy,  109  ;  potentials 
within,  123  ;  best  position  for  on  leaky 
line,  131,  132  ;  internal  resistance  of, 
methods  of  measuring,  207. 

Battery  materials,  choice  of,  20. 

Battery  solutions,  table  of  specific  gravities 
of,  9. 

Baume's  hydrometer  scale,  7. 

Becker's  experiments  on  resistances  of 
liquids,  62,  63. 

Benoit  on  specific  resistance  of  metals,  refer- 
ence to,  57. 

Bichromate  of  potash  cell,  23. 

Bidwell,  Shelford,  on  maximum  magnetic  at- 
traction, 26. 

Binding  screws,  different  patterns  of,  50. 

Biographical  notices : 

Ampere,  Andre  Marie,  60. 

Coulomb,  Charles  Augustin  de,  61. 

Faraday,  Michael,  73. 

Gauss,  Karl  Friednch,  83, 

Henry,  Joseph,  80. 

Joule,  James  Prescott,  63. 

Lefferts,  Marshall,  214. 

Morse,  Samuel  Finley  Breese,  vi. 

Ohm,  Georg  Simon,  62. 

Vail,  Alfred,  216. 

Volta,  Alessandro,  61. 

Watt,  James,  73. 

Blavier's  Telegraphic  Electrique,  reference 
to,  17,  128. 

Bonsanquet,  R.  H.  M.,  on  magneto-motive 
force,  reference  to,  81. 

Boston  screw-glass  insulator,  tests  of  effi- 
ciency of,  120. 

Bottone  s  Electrical  I  nstrument-making  for 
Amateurs,  extracts  from,  46. 

Box  sounder,  144 ;  use  of  in  railway  service, 
144. 

Bradley,  L.,  on  Hill's  gravity  cell,  17. 

Branch  circuit  connection,  diagram  of,  104. 

Branch  or  derived  circuits,  69 ;  rule  for  joint 
resistance  of,  66. 

Brass,  specific  resistance  of,  57. 

Break  or  disconnection,  conditions  arising 
from,  190. 

Breakage  of  battery  jars,  causes  of,  10. 

Bridge,  Wheatstone's,  195 ;  theoretical  ar- 
rangement of,  195  ;  invented  by  Christie, 
195;  principle  of  illustrated,  196;  best  ra- 
tio of  electromotive  forces  and  resistances 
in,  196 ;  actual  construction  of,  198  ;  gal- 
vanometer for.  198  ;  methods  of  making 
various  tests  with,  199-208. 


British  association   ohm,  determination    of, 

62,  63 ;  value  of,  62. 
British  standard  wire-gauge,  95. 
Brooks,    David,  on   effects  01   climate  upon 

telegraphic  insulation,   119;  on  effects  ol 

smoke  in  cities  on  insulation,  119  ;  tests  ot 

various  kinds  of  insulators  by,  120. 
Brooks's  paraffin  insulator,  tests  of  efficiency 

of,  120. 
Brown    &    Sharpe     M'f'g    Co.'s    American 

standard  wire-gauge,  95. 
Brushes  of  dynamo-electric  machine,  168. 
Bunsen's  nitric-acid  cell,  23, 
Button  repeater,  the,  162 ;    management  of, 

165. 

CABLE,  submarine,  diagram  of,  104. 

Caliper,  micrometer,  tor  gauging  wires,  96. 

Callaud's  cell,  17. 

Calorimeter,  the,  44. 

Canada,  closed  circuit  used  in,  108. 

Capacity,  inductive  or  electrostatic,  72  ;  defi- 
nition of,  72  ;  unit  of,  73. 

Cavendish's  theory  of  electricity,  2. 

Cell,  gravity,  maintenance  of,  14 ;  disman- 
tling of,  16  ;  best  adapted  to  closed  cir- 
cuits, 16  ;  waste  products  of,  17  ;  electro- 
motive force  of,  74  ;  resistance  of,  74. 

Cell,  usual  internal  resistance  of,  64  ;  elec- 
trical dimensions  of,  74. 

Cell,  oxide  of  copper,  21. 

Cell,  sulphate  of  copper,  effect  of  tempera- 
ture upon  resistance  of,  78. 

Cell,  voltaic,  Hill's,  Callaud's,  Minotto's, 
Thomson's,  17 ;  Lockwood's.  18 ;  Dan- 
iell's,  19  ;  Edison-Lalande,  21  ;  Grove's, 
23  ;  Bunsen's,  23 :  rate  of  consumption  of 
material  in,  13  ;  effect  of  continued  action 
in,  13;  various  forms  of,  17  ;  general  direc- 
tions for  care  of,  20 ;  how  shown  in  dia- 
gram, 104. 

Centimetre,  the  unit  of  space,  37. 

Centimetre-gram-second  system  of  units,  37  ; 
units  of  force  and  work,  37. 

Chaperon,  G.,  and  F.  de  Lalande,  on  voltaic 
batteries,  23. 

Characters,  code,  exercises  with,  220. 

Charge,  electrostatic,  177  ;  current  of,  177. 

Chemical  atomic  weights  of  battery  materials, 
table  of,  8. 

Chemical  electricity,  3. 

Chemical  equivalents,  table  of,  75. 

Chemical  law  of  definite  proportion,  6. 

Chemical  reaction  of  voltaic  cell,  6  ;  in  closed 
circuit,  12. 

Chemistry  of  voltaic  effect,  6. 

Circuit,  conducting,  effect  of  increasing  the 
length  of,  54. 

Circuit,  closed,  the,  12 ;  chemical  reactions 
in,  12 ;  theoretical  diagram  of,  12. 

Circuit,  distribution  of  potentials  in  when  in- 
sulated, 120. 

Circuit,  electric,  constituent  parts  of,  n; 
formation  of,  n;  nomenclature  of,  12; 
graphic  illustration  of.  71. 

Circuit,  external,  the,  12 ;  internal,  the,  12. 

Circuit,  imperfectly  insulated,  distribution  of 
potem.als  in,  125. 

Circuit,  magnetic,  80 ;  conception  of  due  to 
Joule,  80. 

Circuit,  open  or  broken,  the,  12. 

Circuits,  telegraphic,  102  ;  open  and  closed, 
102;  diagram  of,  104;  essential  character- 
istics of,  102;  general  considerations  re- 
specting, 109;  working  efficiency  of,  in  ; 
distribution  of  potentials  in,  120. 

Circuits  of  American  telegraphic  system,  ar- 
rangement of,  151. 


Index. 


227 


Clamp-screw  of  gravity  cell,  4. 

Clark,  Latimer,  on  Wheatstone's  bridge, 
196  ;  provisional  theory  of  electricity,  58. 

Clark's  Electrical  Measurement,  references 
to,  125,  198 ;  extract  from,  58. 

Clerk-Maxwell,  theory  pt  electricity,  2. 

Climate,  effect  of  upon  insulation,  118. 

Clip,  the,  in  diplex  and  quadruplex  telegraph, 
how  obviated,  184. 

Closed  and  open  circuit  systems  of  teleg- 
raphy, comparative  advantages  of,  109. 

Closed-circuit  system  of  telegraphy,  102  ; 
description  of,  108  ;  American  modification 
of,  108  ;  position  of  battery  in,  109. 

Coast  survey  report,  reference  to,  99. 

Cobalt,  magnetic  properties  of,  24. 

Code,  telegraphic,  formation  of,  216 ;  ele- 
mentary principles  of,  219. 

Code,  American  Morse,  217,  218  ;  alphabet 
and  numerals  of,  218 ;  punctuation,  etc., 
of,  218 ;  best  method  of  learning,  219 ; 
exercises  with,  220. 

Coil  or  loose  bundle  of  wire,  how  shown  in 
diagram,  104. 

Combinations  of  permanent  and  electro-mag- 
nets, 100. 

Commutator  of  dynamo-electric  machine, 
function  of,  167  ;  construction  of,  168. 

Compass,  magnetic,  25. 

Condenser,  construction  of,  178 ;  application 
of  to  duplex  telegraph,  178 ;  first  applied 
by  Stearns,  178 ;  how  shown  in  diagram, 
104. 

Conducting  circuit,  an  element  of  the  electric 
telegraph,  2. 

Conductivity  resistance,  relation  of  insula- 
tion to,  no  ;  of  line,  measurement  of  with 
bridge,  199. 

Conductors,  insulated,  for  interior  construc- 
tion, 114;  telegraphic,  m. 

Conductors  and  insulators,  characteristics  of, 
56 ;  tible  of,  57. 

Connecting  wire  in  gravity  battery,  protec- 
tion of,  ii. 

Conservation  of  force,  principle  of  ex- 
plained, 38. 

Constancy,  value  of  in  voltaic  cell,  74. 

Constant  of  galvanometer,  method  of  deter- 
mining, 206. 

Consumption  of  material  in  cell  in  relation  to 
electricity  evolved,  17. 

Contraplex  and  diplex  methods,  combination 
of,  184. 

Conventional  representation  of  circuits  and 
apparatus,  103,  104,  105. 

Cooke's  New  Chemistry,  extract  from,  6. 

Copper,  chemical  equivalent  of,  75. 

Copper  connector,  of  gravity  cell,  5. 

Copper  plate,  of  gravity  cell,  4 ;  modifi- 
cations of,  10 ;  the  negative  element  of,  12. 

Copper  line  wires,  114  ;  table  of  dimensions 
and  qualities  of,  112. 

Copper  sulphate,  chemical  analysis  of,  8. 

Copper  wire,  bare,  for  magnet  helices,  94 ; 
hard  drawn,  table  of  sizes,  weights,  resist- 
ances, etc.,  112. 

Core  of  electro-magnet,  91. 

Core,  diameter  of  in  electro-magnet,  force  of 
attraction  affected  by,  87 ;  best  proportions 
for,  91. 

Cost  of  materials  consumed  in  battery,  74 ; 
of  battery  maintenance,  method  of  deter- 
mining, 75. 

Coulomb,  Charles  Augustin  de,  biographical 
notice  of,  61. 

Coulomb,  the  unit  of  electrical  quantity,  defi- 
nition of,  61. 

Cross,    definition    of,    190 ;    metallic,    191 ; 


swing,  ,191 ;  weather,  191 ;  method  of  test- 
ing tor,  193  ;  principle  ot  test  for,  193. 

Cross,  on  line,  locating  position  of,  204. 

Cross-arms,  tests  of  insulating  value  of,  133, 
134. 

Cross-current,  remedy  for,  132. 

Cross-tire,  191  ;  explanation  of  cause  ot,  132  j 
remedy  tor,  132. 

Crossing  of  two  wires,  representation  of  in 
diagram,  104. 

Cross-section  of  body,  effect  of  upon  resist- 
ance, 58. 

Current,  alternating,  of  dynamo-machine, 
167. 

Current,  electric,  formation  of,  n  ;  produced 
by  magnetic  held,  29  ;  manifestations  of  in 
conductor,  35  ;  effect  of  imperfect  insula- 
tion upon  now  of,  127  ;  direction  of,  how 
shown  in  diagram,  $04. 

Current  lorce,  relation  of  to  mechanical  force, 

'to- 
Current  induction,  74. 

Current,  inducing  or  primary,  74  ;  direction 
of,  31. 

Current,  induced  or  secondary,  31,  74. 

Current  in  leaky  lines,  128;  taDle  tor  com- 
puting, 129. 

Current  of  charge  on  insulated  line,  177. 

Current  of  dynamo-electric  machine,  charac- 
teristics of,  167. 

Current,  relation  of  to  magnetic  force,  85  ; 
self-induction  of,  98  ;  in  coiled  conductor, 
98. 

Currents,  adaptation  of  electro-magnets  to, 
96  ;  method  of  determining,  96  ;  distribu- 
tion of  in  quadruplex  telegraph,  186. 

Currents,  earth,  disturbing  influence  of  on 
conductivity  tests,  201. 

Currents  of  charge  and  discharge,  effects  of 
on  line,  177. 

Currents,  received,  test  of  insulation  by 
means  of,  208. 

Curve,  of  ratio  between  magnetic  attraction 
and  distance,  90  ;  of  electrical  dimensions 
in  oxide  of  copper  cell,  77  ;  of  resistance 
as  affected  by  temperature  in  Daniell's 
cell,  79  ;  of  magnetization  of  soft  iron, 
85  ;  of  magnetic  saturation,  85  ;  of  poten- 
tials in  electric  circuits,  121,  123,  124;  of 
potential  within  battery,  125  ;  of  potential 
on  leaky  line,  125,  126,  130. 

Cut-out  wedge,  the,  155. 

DANIELL'S  Principles  of  Physics,  extract 
from,  2  ;  reference  to,  38. 

Daniell's  sulphate  of  copper  cell,  18 ;  main- 
tenance of,  19 ;  renewal  of,  19. 

Davis,  Daniel,  Jr.,  experiments  on  magnetic 
attraction.  89,  90. 

Davis's  Manual  of  Magnetism,  reference  to, 
89. 

Dead  ground,  definition  of,  190. 

Dean,  G.  W.,  experiments  of  on  self-induc- 
tion and  hysteresis  in  telegraph  magnets, 

QQ. 

Deflections,  proportional,  measuring  high  re- 
sistances by  method  of,  205. 

De  Lalande,  F.,  and  G.  Chaperon,  on  voltaic 
batteries,  23. 

Density,  magnetic,  83. 

Derived  and  fundamental  units,  37. 

Derived  or  branch  circuits,  69. 

Detector  or  galvanpscope,  41. 

Diagrams  of  electric  apparatus,  103. 

Differential,  electro  magnet,  principle  of,  171 ; 
galvanometer,  construction  and  use  of, 
208. 

Diffusion  of  solution  in  gravity  cell,  16. 


228 


Index. 


Dimensions,  electrical,  of  voltaic  cell,  74. 

Diplex  telegraphy,  171. 

Diplex,  principle  of,  182 ;  receiving  appara- 
tus of,  183  ;  clip  in,  184 ;  short  core  relay 
for,  184. 

Diplex  and  contraplex,  combination  of,  to 
form  quadruple*,  184. 

Direction  of  electric  current,  purely  a  con- 
ventional assumption,  12. 

Disconnection  or  break,  conditions  arising 
from,  190 ;  testing  for,  191  ;  testing  for  at 
way  station,  154  ;  causes  of,  192. 

Disconnection,  partial,  190 ;  testing  for,  192. 

Distance  between  magnet  and  armature,  ef- 
fect of  upon  attractive  force,  89 ;  experi- 
mental determination  of,  and  tabulated 
results,  89,  90. 

Dot,  an  element  of  telegraphic  code,  216  ;  the 
unit  of  time  and  space  in  ditto,  217. 

Double  current  duplex,  apparatus  of,  180. 

Double  current  or  reversing  key,  180;  how 
shown  in  diagram,  104. 

Double  measurement,  process  of  in  line  test- 
ing, 203. 

Drawings,  of  electric  apparatus,  103 ;  per- 
spective, 103 ;  geometrical,  103. 

Duplex  telegraphy,  171. 

Duplex,  single  current,  172 ;  apparatus  of, 
172  ;  circuits  of,  173  ;  artificial  line  of,  173; 
balancing  of,  173 ;  effect  of  currents  of 
charge  and  discharge  in,  177  ;  ground  and 
spark  coils  of,  179 ;  double  current,  de- 
scription of,  180. 

Duration  of  cell,  considerations  affecting,  74. 

Dynamo  current,  characteristics  of,  167  ;  ap- 
plication of  to  quadruples  telegraphy, 
185,  186. 

Dynamo-electricity  defined,  24. 

Dynamo-electric  generator,  employment  of 
in  telegraphy,  167. 

Dynamo-electric  machine,  the,  32  ;  theory  of 
explained,  32  ;  diagram  of,  104  ;  field  of, 
168  ;  commutator  of,  168  ;  brushes  of,  168 ; 
characteristics  of,  169  ;  Edison's,  168  ;  ar- 
rangement of  in  potential  series,  169;  posi- 
tive and  negative  series  of,  170 ;  capacity 
of,  171 ;  shunt  coils  of,  arrangement  of  in 
telegraphy,  171. 

Dynamos,  arrangement  of  in  series  in  New 
York  station,  170. 

Dyne,  unit  of  force,  definition  of,  38. 

EARTH,  the,  an  electrical  cpnductor,  104; 
magnetism  of,  40 ;  field  offeree  due  to,  40. 

Earth  circuit,  principle  of,  106 ;  advantages 
of,  106. 

Earth  or  ground  plate,  how  shown  in  dia- 
gram, 104 ;  precautions  in  fixing,  106. 

Earth  currents,  disturbing  influence  of  on 
conductivity  tests,  201 ;  how  eliminated, 

201. 

Edison,  T.  A.,  inventor  of  method  of  diplex 

-      transmission,  185. 

Edison's  dynamo-electric  machine,  168,  169. 

Edison-Lalande  oxide  of  copper  cell,  21  ; 
electromotive  force  and  resistance  of,  76  ; 
duration  of,  76 ;  chart  of  electrical  dimen- 
sions of,  77. 

Effect  of  continued  action  on  voltaic  cell,  13. 

Efficiency,  working,  of  lines,  importance  of 
high,  135 ;  best  method  of  improving,  135  ; 
examples  of  advantageous  results  of,  135, 
136;  of  telegraphic  circuit,  in  ;  computa- 
tion of,  128. 

Electric  circuit,  formation  of,  n  ;  graphic  il- 
lustration of,  71. 

Electric  current,  manifestations  of  in  con- 
ductor, 35 ;  produced  by  magnetic  field,  29. 


Electric  field  of  force,  39. 

Electrical  action,  laws  and  conditions  of,  45 ; 

mechanical  analogue  of,  58. 
Electrical  and  magnetic  units,  derivation  of, 

Electrical  and  mechanical  force,  statement 
of  law  connecting,  59. 

Electrical  Engineer  (N .  Y.),  references  to,  23, 
74  ;  extract  from,  2. 

Electrical  measurement,  quantitative,  theory 
of,  35  ;  importance  of,  36. 

Electrical  Re-view  (London),  reference  to,  23. 

Electrical  II  orld,  relerence  to,  185. 

Electrician  (London),  reference  to,  81. 

Electrician  and  Electrical  Engineer ^  refer- 
ences to,  87,  94. 

Electricity,  chemical,  3  ;  magneto,  24  ;  dyn- 
amo, 24  j  t  rictional,  33  ;  static,  33  ;  ther- 
ruo,  34. 

Electricity,  theories  of  nature  of,  2  ;  origin 
of,  3  ;  sources  of,  3  ;  characteristics  of  capa- 
ble of  measurement,  43;  apparatus  re- 
quired for  measurement  of,  43 ;  provisional 
theory  of,  58 ;  production  ot  in  battery  in 
proportion  to  material  consumed,  76. 

Electricity  and  magnetism,  essential  nature 
of,  2. 

Electrification,  72. 

Electro  and  permanent  magnets,  combina- 
tions Of,  101. 

Electro-chemical  equivalent,  of  zinc,  74,  75  ; 
of  copper,  75  ;  ot  copper  sulphate,  75. 

Electrodes  of  cell  defined,  12. 

Electrolysis  of  liquids  by  electric  current,  36. 

Electro-magnet,  the,  80 ;  its  modern  form  in- 
vented by  Henry,  80  ;  polarity  of  deter- 
mined by  direction  of  current,  81  ;  ele- 
ments of,  81  ;  adaptation  of  to  working 
currents,  96  ;  spectrum  of,  96,  97  ;  indirect 
causes  of  retardation  in,  99 ;  with  polar- 
ized armature,  xop  ;  differential,  principle 
of,  171 ;  construction  of,  172. 

Electro-magnetism,  32  ;  laws  of,  80. 

Electromotive  force,  conception  of,  59 ;  of 
ordinary  gravity  cell?  74. 

Electrostatic  or  inductive  capacity,  72 ;  of 
line,  175. 

Electrostatic  accumulation  upon  insulated 
conductor,  177. 

Electrostatic  balance  of  duplex  telegraph, 
178. 

Elements  of  electric  telegraph,  2  ;  of  electro- 
magnet, 81. 

Endcvmose,  action  of  in  voltaic  cells,  20. 

English  unit  of  magnetic  induction,  83. 

Equator  of  magnet,  26. 

Equipment  of  American  telegraph  lines,  138. 

Equivalent,  of  mechanical  energy,  31  ;  elec- 
trical and  mechanical,  definition  of,  38. 

Erg,  unit  of  work,  definition  of,  38. 

Escape  or  leakage  on  line,  190 ;  testing  for, 
192;  <n  line,  locating  position  of,  202; 
ditto  by  double  measurement,  203 ;  by  loop 
test,  203. 

European  register,  148. 

Evaporation  in  battery  cells,  prevention  of, 
10,  14. 

Everett's  Units  and  Physical  Constants,  refer- 
ence to,  38. 

Ewing's  researches  in  magnetism,  98. 

Exercises  with  code  characters,  220,  221. 

External  circuit,  the,  defined,  12. 

FALL  OF  POTENTIAL,  illustrated,  70  ;  propor- 
tionate to  fall  of  resistance  along  con- 
ductor, 71. 

Farad,  the  unit  of  electrostatic  or  inductiev 
capacity,  73. 


Index. 


229 


Farad  .y.  Michael,  biographical  notice  of,  73. 

Faraday  s  theory  of  electricity,  2  ;  discovery 
of  magneto-electricity,  29  ;  Experimental 
Researches^  references  to,  3,  29 ;  lines  of 
magnetic  force,  27,  28. 

Farmer,  M.  G.,  on  resistances  or'  battery  so- 
lutions, 62 ;  observations  on  earth  circuit 
as  affected  by  character  of  soil,  107  ;  on 
effects  of  wet  upon  telegraphic  insulation, 
119 ;  on  working  efficiency  of  telegraph 
lines,  128;  table  of  percentages  of  received 
current  on  telegraph  lines,  136. 

Fault  in  line,  effect  of  position  of,  131. 

Faults  and  interruptions,  classification  of, 
190. 

Field,  electro-magnetic,  of  dynamo  machine, 
168. 

Field,  magnetic,  the,  27. 

Field,  magnetic,  lines  of  force  a  measure  of, 
82. 

Field  of  force,  electric,  39. 

Field  of  magnetic  force,  properties  of,  how 
determined,  27. 

Field,  Stephen  D.,  inventor  of  application  of 
dynamo  to  telegraphy,  185. 

Flux,  magnetic,  88. 

Force,  conservation  of,  doctrine  of,  ex- 
plained, 38. 

Force,  definition  of,  27 ;  lines  of,  a  measure 
of  magnetic  field,  82  ;  relation  of  current 
to  mechanical,  40  ;  unit  of,  defined,  37. 

Formation  of  the  electric  circuit,  n. 

Franklin's  theory  of  electricity,  2. 

French,  E.  L.,  on  electro-magnetic  attrac- 
tion, 87. 

Frictional  electricity,  33. 

Fundamental  and  derived  units,  37. 

Fundamental  units  of  mass,  space  and  time, 
36. 

GALVANIC  ELEMENT,  the,  3. 

Galvanized  iron  wire,  table  of  sizes,  weights 
and  resistances  of,  112. 

Galvanometer,  the,  41  ;  how  shown  in  dia- 
gram, 104  ;  astatic,  200  :  differential,  con- 
struction of,  208  ;  for  Wneatstone  bridge, 
198. 

Galvanometer,  tangent,  41,  209;  construction 
of,  41  ;  use  of  in  testing  insulation  by 
received  currents,  209  ;  in  experimental 
investigations,  52 ;  table  of  tangents  for, 

Galvanometer,  taking  constant  of,  206  ;  re- 
sistance of,  method  of  measuring,  208  ;  ap- 
plication of  snunts  to,  205. 

Galvanoscope,  the,  41 ;  how  shown  in  dia- 
gram, 104. 

Gap  in  magnetic  circuit,  effect  of,  89. 

Gas  and  water  pipes  used  for  ground  con- 
nections, 106. 

Gauging  wire,instruments  for,  95. 

Gauss,  Karl  Friedrich,  biographical  notice 
of,  83. 

Gauss,  the  proposed  unit  of  magnetism,  83  ; 
definition  of,  83. 

Gauss  anJ  Weber's  electric  telegraph,  83. 

Gavarret's  Telegraphic  Eiectrique,  reference 
to,  128. 

Generator,  the,  an  element  of  electric  tele- 
graph, 2. 

German-silver,  specific  resistance  of,  57. 

Glass  insulator,  the,  115;  defects  of,  115; 
tests  of,  120,  134. 

Glass  jar  of  battery  cell,  4  ;  breakage  of,  how 
avoided,  10. 

Gram,  the  unit  of  mass  or  weight,  37. 

Gravity  cell,  description  of,  4;  installation  of, 
9  ;  formula  for  preparing  solutions  for,  8. 


Gray's  Absolute  Measurements  in  Electricity 
and  Magnetism,  reference  to,  40. 

Ground  or  earth  plate,  how  shown  in  dia- 
gram, 104  ;  at  distant  station,  measuring 
resistance  of,  202  ;  defective,  effect  ot,  191. 

Ground  connection,  how  made,  106  ;  precau- 
tions in  making,  106. 

Ground,  on  line,  190  ;  locating  position  of, 
202. 

Ground  and  spark  coils  in  duplex  telegraph, 
179. 

Grove's  nitric  acid  cell,  23. 

HANGER  OF  GRAVITY  BATTERY  CELL,  4. 

Hardening  of  magnet  cores  objectionable,  99, 

Hard  iron  and  steel,  magnetic  properties  of, 
24. 

Hard-rubber  insulator,  the,  117. 

Healy,  Clarence  L.,  on  quadruplex  teleg- 
raphy, 187. 

Heat,  development  of  by  electric  current, 
36;  effect  of  upon  e.  m.f.  of  sulphate  of 
copper  cell,  74. 

Helices  of  electro-magnets,  machine  for 
winding,  93  ;  thickness  of  spaces  between 
wires  of,  94  ;  of  bare  copper  wire,  94. 

Helix,  magnetic,  effect  of  iron  in,  84;  effect 
of  position  of  windings  in,  92  ;  construc- 
tion of,  92  ;  relation  of  number  of  turns  to 
thickness  and  length  of  wire  in,  92  ;  num- 
ber of  turns  in,  measured  by  its  resist- 
ance, 93. 

Henning,  Thomas,  on  quadruplex  telegraphy, 
187. 

Henry,  Joseph,  biographical  notice  of,  80. 

Henry's  theory  of  electricity,  2. 

Hering,  Carl,  on  lines  of  magnetic  force,  82. 

Her  ing's  Principles  of  Dynamo- Electric  Ma- 
chines, extract  from,  82. 

High  resistances,  methods  of  measuring,  305. 

Hill,  E.  A.,  on  the  voltaic  cell,  17. 

Hill's  cell,  17. 

Hints  to  learners,  216. 

Horizontal  component  of  earth's  magnetism, 
defined,  40 ;  value  of  in  various  parts  ot 
North  America,  40. 

Horseshoe,  magnet,  26  •  electro-magnet,  87. 

Hughes,  Prof.  D.  E.,  theory  of  magnetism, 
•  24. 

Hydrogen,  evolution  of  in  voltaic  cell,  5. 

Hydrometer,  the,  description  of,  7. 

Hysteresis,  magnetic,  definition  of,  97;  effect 
of  on  telegraph  magnets,  99. 

INDUCED  OR  SECONDARY  CURRENT,  74;  direc- 
tion of,  31. 

Inducing  or  primary  current,  74. 

Induction,  current,  74  ;  static,  175,  177;  mag- 
netic, phenomena  of,  25  ;  magnetic,  cause 
of,  85. 

Induction  of  current  upon  itself.  98. 

Inductive  or  electrostatic  capacity,  72. 

Inertiat  magnetic,  definition  ot,  99. 

Ink-writing  register,  150. 

Installation  of  gravity  cell,  9. 

Instrument  tables,  160. 

Insulating  value  of  wet  poles  and  cross-arms, 
tests  of,  133,  134. 

Insulation,  imperfect,  effects  of,  no  ;  defec- 
tive of  American  lines,  118  ;  effects  of  cli- 
mate upon,  118  ;  effect  of  upon  flow  of 
current,  127  ;  Farmer's  table  of,  136. 

Insulation  resistance  of  line,  measurement  of, 
202  ;  relation  of  conductivity  to,  no. 

Insulation,  test  of,  by  received  currents,  208. 

Insulator,  glass,  Western  Union,  old  pattern, 
116 ;  new  standard  pattern,  i  r6  ;  hard  rub- 
ber, 117;  paraffin,  117  ;  porcelain,  118. 


230 


Index. 


Insulators  and  conductors,  characteristics  ot, 
56  ;  comparative  table  of,  57. 

Insulators,  telegraphic  line,  115;  common 
glass,  115  ;  defects  of,  115;  resistance  of 
influenced  by  form,  116;  comparison  of 
different  forms  ot,  116;  tests  of,  120,  134; 
measurement  of  resistance  of,  206  ;  value 
of  wu  poles  and  cross-arms  considered  as, 
133. 

Intensity,  of  magnetization  defined,  86  ;  of 
magnetic  field  denned,  27. 

Intermingling  ot  currents  on  telegraph  lines, 
132. 

Internal  circuit,  the,  defined,  12. 

Internal  resistance  of  battery,  methods  of 
measuring,  207. 

Interruptions  and  faults  on  telegraph  lines, 
classification  of,  190. 

Iron,  magnetization  of  by  electric  current, 
35  ;  specific  electrical  resistance  of,  57  ;  ef- 
fect of  in  magnetic  helix,  84. 

Iron  filings  held  to  conductor  by  magnetism, 

Iron  wires  for  lines,  table  of  sizes,  weights, 

and  resistances  ol,  112  ;  joints  in,  113. 
Iron  and  steel,  magnetic  properties  of,  24. 

JENKIN,  FLEEMING,  on  conductors  and  insula- 
tors, 56  ;  on  Wheatstone's  bridge,  198. 

Jenkin's  Electricity  and  Magnetism,  refer- 
ences to,  17,  18,  62,  198. 

Johnson's  Universal  Cyclopedia,  reference  to, 

20. 

Joint,  detective,  on  line,  method  of  locating, 
205. 

Joint,  twist,  for  iron  wires,  113;  importance 
of  soldering.  113. 

Joint  resistance  of  branch  circuits,  rule  for 
determining,  66. 

Jones,  Francis  W.,  on  quadruplex  teleg- 
raphy, reference  to,  187. 

Joule,  James  Prescott,  biographical  notice 
of,  63. 

Joule's  law,  statement  of,  63. 

Joule's  conception  ot  magnetic  circuit,  81. 

KAPP  LINE,  the,  83. 

Kapp's  Electric  Transmission  of  Energy, 
reference  to,  24. 

Kapp's  unit  of  magnetic  induction,  83  ;  value 
of,  83. 

Kempe,  A.  B.,  on  the  leakage  of  submarine 
cables,  reference  to,  128. 

Kempe,  H.  R.,  Handbook  of  Electrical  Test- 
ing, references  to,  128,  198 ;  on  Wheat- 
stone's  bridge,  198. 

Kennelly  and  Wilkinson's/Vvz<r//cYi/ Notes for 
Electric  Students,  reference  to,  85. 

Kerite  insulation  for  office  wires,  113,  114. 

Key,  construction  of,  138  ;  adjustment  of, 
140 ;  platinum  contacts  of,  138  ;  modifica- 
tions of,  139 ;  Western  Electric  pattern, 
140;  Victor  pattern,  140;  double-current 
or  reversing,  180  ;  common  Morse,  how 
shown  in  diagram,  104  ;  three-point,  how 
shown  in  diagram,  104  ;  method  of  hand- 
ling, 219  ;  preliminary  practice  with,  220. 

Key  and  sounder,  combination,  143  ;  pocket, 

1 44- 
Key,  relay,  and  register,  combination  of,  149. 

Kick,  due  to  electrostatic  charge  and  dis- 
charge, 177. 

Kohlrausch's  Physical  Measurement,  refer- 
ence to,  62. 

LAW  OF  MAGNETIC  CIRCUIT,  88. 

Law  of  electric  current,  Ohm's,  63 ;  Joule's, 
63. 


Law  connecting  mechanical  and  electric 
force,  59. 

Learners,  hints  to,  216. 

L"  Electrician,  reference  to,  23. 

Lefferts,  Marshall,  biographical  notice  of,  214. 

Legal  ohm,  determination  of,  63 ;  value  of,  63. 

Length  of  body,  effect  of  upon  resistance,  58. 

Letter  space,  an  element  of  telegraphic  code, 

216. 

j  Lightning  arrester,  description  of,  160;  com- 
bination of  with  switch,  156,  157;  inspec- 
tion and  care  of,  161 ;  how  shown  in  dia- 
gram, 104. 

j  Line,  computation  of  working  efficiency  of, 
128  ;  electrostatic  capacity  of,  175 ;  over- 
head, diagram  of,  104  ;  submarine  or  sub- 
terranean, diagram  of,  104  ;  artificial,  of 
multiple  telegraph,  174. 

|  Lines,  leaky,  resistance  and  current  in,  128 ; 
table  for  computing  resistances  and  escapes 
upon  various  lengths  of,  129  ;  best  position 
for  battery  on,  131,  132 ;  effect  of  pos.tion 
of  fault  in,  131. 

Lines  of  magnetic  force,  conception  of  due  to 
Faraday,  27  ;  rendered  visible  by  iron 
filings,  27. 

Local  circuit,  working  by  relay  and,  144. 

Lockwood  cell,  description  of,'  18. 

Lockwood's  Electricity,  Magnetism,  and 
Electric  Telegraphy,  references  to,  23,  34. 

Lodestone  or  natural  magnet,  properties  of, 
24. 

Lodge,  Oliver  J,,  theory  of  electricity,  2. 

Loop  test  for  conductivity  resistance,  201 ; 
for  position  of  escape,  203 ;  Varley's  mod- 
ification of,  203. 

MAGNET,  bar,  24 ;  horseshoe,  26  ;  multipolar, 
26 ;  natural  and  artificial,  24  ;  temporary 
and  permanent,  24. 

Magnet,  polarity  of,  25 ;  magnetic  length  of, 
26  ;  maximum  attraction  exerted  by,  26. 

Magnet,  telegraph,  best  proportions  for,  91 ; 
details  of  construction  of,  91. 

Magnet  wires,  Prescott's  table  of  dimensions 
and  resistances  of,  93. 

Magnetic  attraction  and  repulsion,  28. 

Magnetic  circuit,  conception  of  by  Joule  and 
others,  81  ;  formation  of,  87 ;  law  of,  88. 

Magnetic  compass,  the,  25. 

Magnetic  density,  83. 

Magnetic  field,  the.  27  ;  exploration  of  by  sus- 
pended needle,  28  ;  of  the  earth,  40. 

Magnetic  flux,  88. 

Magnetic  force,  relation  of  current  to,  85. 

Magnetic  hysteresis,  definition  of,  97. 

Magnetic  induction,  phenomena  of,  25;  cause 
of,  85. 

Magnetic  inertia,  definition  of,  99. 

Magnetic  length  of  magnet,  26. 

Magnetic  meridian,  the,  24,  28. 

Magnetic  moment,  definition  of,  86;  experi- 
mental determination  of,  86  ;  tabulated  re- 
sults of,  86. 

Magnetic  needle,  the,  24. 

Magnetic  permeability,  88  ;  definition  of,  88. 

Magnetic  reluctance,  88;  determination  of, 
88. 

Magnetic  resistance,  88. 

Magnetic  saturation,  curve  of,  85;  definition 
of,  87. 

Magnetic  spectrum,  the,  26. 

Magnetic  and  electrical  units,  derivation  of, 

characteristics 


Magnetism,  definition  of, 
of,  24 ; 
of, 
remanent  or  residual,  98. 


rnetism,  definition  ol,  24  ;  characteristics 
f,  24 ;  unit  of,  83  ;  intensity  of,  83 ;  density 
f ,  83  ;  lines  of  force  a  measure  of,  82 ; 


Index. 


Magnetism  and  electricity,  essential  nature 
of,  2. 

Magnetization,  of  one  body  by  another,  25; 
intensity  of  defined, 86 ;  proportional  to 
ampere-turns,  87 ;  maximum  limit  of  in 
soli  iron,  87. 

Magneto-electricity,  3 ;  definition  of,  24 ; 
phenomena  of,  summarized,  32. 

Magneto-motive  torce,  81,  83;  definition  of, 
83  ;  method  of  computing,  84. 

Magnetometer,  construction  and  use  of,  85. 

Maintenance  of  voltaic  cell,  14. 

Manual  and  automatic  repeaters,  162. 

Manuscript  copy,  practice  from  recom- 
mended, 222. 

Materials  consumed  in  battery,  quantity  and 
cost  of,  74. 

Matthiessen  on  specific  resistance  of  metals, 
reference  to,  57. 

Maver,  William,  jr..  on  dynamo  telegraphy, 
185  ;  on  quadruplex  telegraphy,  187. 

Maximum  magnetic  effect  in  electro-magnet, 
best  proportions  for,  91. 

Mayer's  Eartk  a  Great  Magnet,  reference  to, 
24. 

Measurement,  absolute  system  of,  37;  quan- 
titative electrical,  theory  of,  35  ;  impor- 
tance of,  36;  electrical,  character  of,  43  ; 
practice  of,  195. 

Mechanical  force,  relation  of  to  current  force, 
40. 

Mechanical  power,  transformation  of  into 
electricity  and  heat,  31. 

Mechanical  analogue  of  electrical  action,  58. 

Megadyne,  definition  of,  38. 

Metallic  cross,  191. 

Metals,  specific  resistance  of,  57. 

Metric  system,  foundation  of  absolute  sys- 
tem of  electrical  and  magnetic  units,  37. 

Mexico,  closed  circuit  used  in,  108. 

Microfarad,  the,  73. 

Micrometer  caliper  for  gauging  wires,  96. 

Milliken's  automatic  repeater,  165. 

Minotto's  cell,  17. 

Modern  Practice  of  Electric  Telegraph  (4th 
ed.),  reference  to,  17,  23. 

Moment,  magnetic,  definition  of,  86. 

Movement  of  conductor  in  magnetic  field, 
effects  of,  30. 

Muller,  on  increase  of  resistance  of  metals  by 
rise  in  temperature,  78. 

Multiple  series  of  cells,  53. 

Multiple  wire  switchboard,  156. 

Multiples  of  electrical  units,  60. 

Multipolar  magnet,  26. 

Munroe  and  Jamieson's  Pocket-book  of  Rules 
and  Tables,  reference  to,  73. 

Mutual  reactions  of  current  and  magnet,  32, 

NEEDLE,  magnetic,  deflected  by  current,  35. 

Needles,  astatic,  system  of,  198. 

Negative  plate  or  element  of  cell,  12. 

Neutral  line  of  magnet,  26. 

Niaudet's  Electric  Batteries,  reference  to,  62. 

Nickel,  magnetic  properties  of,  24. 

Nipher's  Theory  of  Magnetic  Measurements, 

reference  toj  40. 

Nomenclature  of  electric  circuit,  12. 
North  pole  and  south  pole  of  magnet,  26. 
North-seeking  pole,  the,  29. 
North  British  Review,  extract  from,  56. 
Nystrom,  J.  W.,  definition  of  force.  27. 
Nystrom's  Elements  of  Mechanics,  extract 

from,  27. 

OFFICB  WIRES,  113  ;   table  of  dimensions  of, 

114. 
Ohm,  Georg  Simon,  biographical  notice  of,  61. 


Ohm,  the  unit  of  electrical  resistance,  defini- 
tion of,  61  ;  value  of,  61,  62,  63. 

Ohm's  law,  statement  of,  63 ;  experimental 
proof  of,  64. 

Oil,  used  to  prevent  evaporation  in  voltaic 
cells,  14. 

Okonite  insulation  for  office  wires,  113,  114. 

Open  circuit,  in  telegraphy,  102,  103  ;  system 
of  telegraphy,  description  of,  107. 

Open  and  closed  circuit,  comparative  advan- 
tages of,  109. 

Operator  and  Electrical  World,  references 
to,  185,  187. 

Origin  ot  electricity.  3. 

Oxide  of  copper  cell,  21  ;  maintenance  of,  22  ; 
chemical  reaction,  22. 

Oxide  of  zinc  formed  by  action  of  voltaic 
cell,  6. 

PARAFFIN  INSULATOR,  the,  117. 

Parallel  arrangement  of  voltaic  cells,  54. 

Parallel  series  of  cells,  53. 

Paris  exposition,  Report  on  Telegraphic  Ap- 
paratus, extract  from,  128. 

Parting  word,  a,  223. 

Permanent  and  temporary  magnets,  24. 

Permanent  and  electro-magnets,  combina- 
tions of,  10 1. 

Permeability,  magnetic,  definition  of,  88 ;  of 
iron,  81. 

Phenomena,  of  voltaic  cell,  5  ;  of  induction 
upon  telegraph  lines,  177. 

Philosophical  Magazine,  reference  to,  81. 

Philosophical  Transactions  of  Royal  Society, 
references  to,  26,  98. 

Physiological  effects  of  electric  current,  36. 

Platinoid,  specific  resistance  of,  57. 

Platinum,  specific  resistance  of,  57. 

Plum,  H.  W.,  on  quadruplex  telegraphy, 
187. 

Pocket  telegraphic  apparatus,  144. 

Polar  or  polarized  relay,  180 ;  how  shown  in 
diagram,  104. 

Polarity  of  the  magnet,  25 ;  of  electro-mag- 
net determined  by  direction  of  current,  81. 

Polarized  armature,  100. 

Pole  changer,  peg,  construction  of,  51. 

Pole-changing  transmitter  in  multiple  teleg- 
raphy, 181. 

Poles  of  magnet,  25  ;  of  voltaic  cell,  12. 

Poles,  tests  of  insulating  value  of  when  wet, 
133,  134. 

Pope,  F.  L.,  on  quadruplex  telegraphy,  187. 

Porcelain  insulator,  the,  118  ;  tests  of,  120. 

Porous  cell,  action  of,  20. 

Position,  method  of  locating,  of  ground,  202  ; 
of  escape,  202  ;  of  cross,  204 ;  of  bad  joint 
or  abnormal  resistance,  205. 

Positive  plate  or  element  of  cell,  12. 

Post-office,  British,  table  of  iron  wires,  112 

Potential,  conception  of.  59 ;  of  telegraph 
line,  determination  of  by  calculation,  123  ; 
of  line,  measurement  of  by  auxiliary  bat- 
tery, 122. 

Potential,  electric,  explanation  of,  69  ;  fall  of 
along  conductor,  illustration  of,  70 ;  pro- 
portionate to  resistance,  71  ;  in  perfectly 
insulated  circuit,  distribution  of,  120 ;  in 
imperfectly  insulated  circuit,  125;  within 
battery,  123. 

Potential  series,  arrangement  of  dynamos  in, 
in  telegraphy,  169. 

Power  or  rate  of  work  of  electric  current,  73. 

Practical  electric  units,  59. 

Practice,  preliminary,  with  key,  220. 

Preece,  W.  H.,  on  effects  of  temperature  on 
sulphate  of  copper  cell,  78,  79. 

Prescott,   Geo.  B..  Jr.,  on  electro-chemical 


232 


Index. 


equivalents,  74 ;  table  of  properties  of  soft 
copper  wires,  112. 

Prescott's  Electricity  and  Electric  Tele- 
graph, reference  to,  62. 

Primary  or  inducing  current,  74. 

Properties  and  dimensions  or  copper  magnet 
wires.  Prescott's  table  of,  94. 

Proportional  deflections,  measuring  high  re- 
sistances by  method  of,  205,  206  ;  measur- 
ing resistance  of  insulators  by,  206. 

QlMDRUPLEX   TELEGRAPHY',  171  \    principle    Of, 

182  ;  a  combination  of  diplex  and  contra- 
plex  systems,  184;  distribution  of  currents 
in,  186  ;  how  worked  by  dynamo  currents, 
185;  practical  management  of,  187;  ad- 
justment of  apparatus  of,  188  ;  repeaters 
for,  189. 

Quantity,  of  current  in  circuit,  conditions 
which  determine,  54 ;  of  material  con- 
sumed in  battery,  74. 

RAIN  WATER,  should  be  used  in  batteries,  5. 

Rate,  of  consumption  of  material  in  voltaic 
cell.  13;  of  work  of  electric  current,  how 
found,  64  ;  relation  of  to  time,  73. 

Reading  by  sound,  222. 

Receiver,  the,  an  element  of  the  electric  tele- 
graph, 2. 

Reciprocals,  66  ;  table  of,  67. 

Reduced  length  of  conductor,  meaning  of,  58. 

Register,  the,  147  ;  construction  of,  147 ; 
European  pattern  of,  148  ;  combination  of 
with  key  and  relay,  149 ;  adjustments  of, 
149 ;  causes  of  defective  marking  in,  150  ; 
ink-writing,  150  ;  how  shown  in  diagram, 
104. 

Relay,  construction  of,  144 :  function  of,  146 ; 
adjustments  of,  147  ;  short  core,  for  diplex 
and  quadruplex  apparatus,  184  ;  polar,  or 
polarized,  180 ;  how  shown  in  diagram, 
104  ;  common  or  non-polarized,  how 
shown  in  diagram,  104. 

Relay  and  local  circuit,  working  by,  144. 

Relay,  key,  and  register,  combination  of,  149. 

Reluctance,  magnetic,  88  :  determination  of, 
88. 

Remanent  or  residual  magnetism,  98. 

Repeater,  the,  162  ;  manual  and  automatic, 
162-  button,  162;  Wood's,  164:  Milli- 
ken  s,  165;  for  duplex,  quadruplex,  and 
multiple  systems,  189. 

Residual  or  remanent  magnetism,  98. 

Resistance,  electrical,  explanation  of,  56; 
conditions  affecting,  58  •  expressible  in 
terms  of  length,  58  ;  artificial,  how  shown 
in  diagram,  104. 

Resistance,  of  circuit,  relation  of  to  quantity 
of  current  flowing  in,  56 ;  abnormal  on 
line,  method  of  locating,  205  ;  relation  of 
conductivity  to  insulation  of  line,  no;  ra- 
tio of  conductivity  to  insulation,  minimum, 
128. 

Resistance,  conductivity,  of  line,  measure- 
ment of  with  bridge,  199. 

Resistance,  insulation,  of  line,  measurement 
of,  202  ;  of  insulators,  method  of  measur- 
ing, 206  ;  of  various  kinds  of  insulators, 
1 20. 

Resistance,  joint,  law  of,  66 ;  of  a  circuit,  how 
to  determine.  66. 

Resistance,  specific,  of  different  metals,  57 ; 
of  copper  wires  for  electro-magnets,  table 
ot,  94 ;  of  galvanized  iron,  hard-drawn 
and  soft  copper  wires,  Prescott's  table  of, 
112  ;  of  metals  emploved  as  conductors  in 
telegraphv,  percentage  of  increase  in  by 
rise  of  temperature,  78. 


Resistance  of  liquids,  Farmer's  values  of,  62; 
Becker's  ditto,  63 ;  of  sulphate  of  copper 
solution,  62,  63 ;  of  sulphate  of  zinc  solu- 
tion, 62,  63  ;  internal,  of  voltaic  cell,  64  ; 
of  ordinary  gravity  cell,  74  ;  of  sulphate 
of  copper  cell,  effect  of  temperature  upon, 
78 :  experiments  of  Preece  on,  78  ;  inter- 
nal, of  battery,  methods  of  measuring,  207. 

Resistance,  very  high,  methods  of  measur- 
ing, 205 ;  of  galvanometers,  method  of 
measuring,  208;  of  helix,  a  measure  of 
number  of  turns  in,  93;  of  leaky  Hues, 

•     128  ;  table  of,  129. 

Resistance  coils,  construction  of,  51. 

Re  istance,  magnetic,  88. 

Retardation  in  electro-magnets,  indirect 
causes  of,  99. 

Reversing  or  double-current  key,  180. 

Rheostat  or  artificial  resistance,  construction 
of,  51 ;  how  shown  in  diagram,  104. 

Ring  gauge,  for  wire,  95. 

Roebling,  J.  A.,  table  of  hard-drawn  copper 
wires,  112. 

Rowland,  H.  A.,  On  Magnetic  Permeability 
of  Iron,  81. 

Royal  Society's  Proceedings,  references  to,  24, 
79- 

SABINE'S  Electric  Telegraph,  reference  to,  83. 

Safety-fuse,  use  of,  161. 

Saturation,  magnetic,  definition  of,  87;  curve 
of,  85  ;  experimental  investigation  of,  86. 

Schott,  C.  A.,  on  determination  of  value  of 
horizontal  component  of  earth's  magnet- 
ism, 40. 

Second,  the  unit  of  time,  37. 

Secondary  or  induced  current,  74. 

Self-exciting  dynamo-electric  machine,  163. 

Self-induction,  effect  of  on  telegraph  mag- 
nets, 99. 

Sentence  space,  an  element  of  telegraphic 
code,  216. 

Series  arrangement  of  voltaic  cells,  52. 

Series  of  cells,  effect  of  varying  number  in, 
53  ;  consumption  of  material  in,  76. 

Shaffner's  Telegraph  Manual,  reference  to, 
62. 

Short-circuiting  a  cell,  8. 

Short-line  sounder,  142. 

Shunt,  definition  and  derivation  of,  69. 

Shunts,  applied  to  galvanometer  for  measure- 
ment of  high  resistances,  205  •  method  of 
using,  206. 

Shunt-wound  dynamo-electric  machine,  168, 
169. 

Siemens'  mercury  unit,  value  of,  62. 

Single-current  duplex,  the,  172. 

Sizes  of  galvanized  iron  and  copper  wires, 
table  of,  112. 

Soft  iron,  effect  of  magnetization  upon,  85 ; 
maximum  limit  of  magnetization  in,  87. 

Soil,  earth  circuit  affected  by  characteristics 
of,  106,  107. 

Sound,  reading  by,  222 ;  methods  of  practice 
in,  223. 

Sounder,  the,  141  ;  adaptation  of  to  short 
lines,  142  ;  adjustment  of,  142;  combina- 
tion kev  and,  143  ;  pocket.  144  ;  box,  144  ; 
how  shown  in  diagram,  104. 

Sources  of  electricity,  3,  24. 

Space,  an  element  of  telegraphic  code,  216. 

Spaced  letters,  formation  of,  222. 

Spaces,  in  helices  of  electro-magnets,  thick- 
ness of,  94. 

Spark  and  ground  coils  in  duplex  telegraph, 
179. 

Specific  gravity,  explanation  of,  7 ;  of  battery 
solutions,  table  of,  9. 


Index. 


233 


Specific  resistance  of  materials,  57  ;  how  de- 
termined, 57. 

Spectrum,  magnetic,  the,  26;  of  electro-mag- 
net, 96. 

Spelter  tor  battery  zincs,  analysis  of,  20. 

Sprague,  J.  T.,  on  effect  of  heat  on  f.  m.f.  of 
sulphate  of  copper  cell,  74. 

Sprague's  Electricity,  extract  from,  74 ;  ref- 
erences to,  38,  57,  62. 

Spring-jack  and  wedge  cut-out,  the,  155  ;  mul- 
tiple ditto.  156. 

Static  or  Irictional  electricity,  33. 

Static  charge  of  line,  nature  of,  177. 

Stearns,  Joseph  B.,  his  inventions  in  duplex 
telegraphy,  178. 

Stewart  and  Gee's  Elementary  Practical 
Physics,  reference  to,  62. 

Stewart's  Conservation  of  Energy,  reference 
to,  38. 

Storage  battery  or  accumulator,  how  shown 
in  diagram,  104. 

Student,  apparatus  required  by,  45. 

Sturgeons  A  nnals,  reference  to,  81. 

Sub-multiples  of  electrical  units,  60. 

Sulphate  of  copper,  chemical  analysis  of,  8  ; 
chemical  equivalent  of,  75  ;  solution,  re- 
sistance of,  62,  63. 

Sulphate  of  zinc,  chemical  analysis  of,  9  ;  so- 
lution, resistance  of,  62,  63. 

Swinging  cross,  191. 

Switch,  universal,  how  shown  in  diagram,  104; 
three-point,  how  shown  in  diagram,  104; 
pole-changing,  how  shown  in  diagram, 

Switchboard,  multiple  wire,  156 ;   universal, 

156;  terminal,  158. 
Switchboard  for  way-station,  description  of, 

152 ;    manipulation    of,    153 ;    testing    by 

means  of,  154. 

TANGENT  GALVANOMETER,  description  of,  41 ; 
principle  of,  42 ;  details  of  construction  of, 
45;  Western  Union  pattern,  209;  use  of 
in  testing  insulation  by  received  currents, 
209. 

Tangents,  natural,  table  of,  55. 

Tapping  upon  key,  importance  of  avoiding, 
219. 

Tap-wire,  in  quadruplex  telegraph,  187. 

Telegraph,  electric,  elements  of,  2. 

Telegraph  lines,  mutual  current  induction 
between,  74  ;  American,  equipment  of, 
138. 

Telegrapher,  The,  extracts  from,  119,  120, 
136;  references  to,  17,  187. 

Telegraphic  circuits,  102  ;  distribution  of  po- 
tentials in,  120. 

Telegraphic  code,  formation  of,  216 ;  ele- 
ments of,  216;  a  multiple  of  time,  216. 

Telegraphic  conductors,  m. 

Telegraphic  magnet,  theoretical  proportions 
of,  91 ;  details  of  construction  of,  91  ; 
spectrum  of,  97 :  effects  of  self-induction 
an<l  hysteresis  in,  99. 

Telegraphy,  multiple,  171  ;  diplex,  171  ;  con- 
traplex,  171  ;  quadruplex,  184. 

Temperature,  effect  of,  on  action  of  voltaic 
cell,  20, 78  ;  on  resistance  of  substances,  58  ; 
effect  of  in  increasing  resistance  of  metals 
employed  as  telegraphic  conductors,  78. 

Temporary  and  permanent  magnets,  24. 

Tensile  strengths  of  galvanized  iron,  hard 
and  soft  copper  wires  for  telegraph  lines, 
table  of,  112. 

Terminal  station,  arrangement  of  apparatus 
at,  158. 

Terminal  switchboard,  158. 

"Testing  telegraph  lines,  190 ;  for  disconnec- 


tion at  way-station,  134  ;  by  quantitative 
measurement,  195  ;  character  of  measure- 
ments in.  195. 

Tests  of  telegraph  lines,  object  of.  190  ;  of 
conductivity  and  insulation,  recording  of, 
214. 

Test-sheets,  Western  Union  Company's 
forms  tor,  212,  213,  214. 

Thermo-electricity,  3,  34. 

Thompson,  Silvanus  P.,  on  magnetic  reac- 
tions, 31  ;  on  Wheatstone's  bridge,  198. 

Thompson's  Elementary  Lessons  in  Elec- 
tricity and  Magnetism,  reference  to,  31, 
198  ;  Dynamo-Electric  Machinery,  refer- 
ence to,  86. 

Thomson,  Sir  William,  on  importance  of 
quantitative  measurement  in  physical 
science,  36;  Popular  Lectures  and  Ad- 
dresses, extract  from.  36. 

Thomson's  theory  of  electricity,  2  ;  cell,  17  ; 
rule  for  computing  the  windings  of  elec- 
tro-magnets, 94. 

Time,  necessarily  involved  in  formation  of 
dot,  217 ;  telegraphic  code  a  multiple  of, 
.216. 

Transmitter,  the,  an  element  of  the  electric 
telegraph,  a. 

Transmitter,  pole  changing,  181 ;  single  cur- 
rent, 173  ;  single  and  double,  how  shown 
in  diagram,  104. 

Transverse  magnetization,  26. 

Trowbridge's  New  Physics,  references  to,  40, 
85. 

Twist-joint  for  iron  wires,  113. 

Tyndall,  observations  on  conservation  of 
energy,  38. 

TyndalPs  Heat  as  a  Mode  of  Motion,  refer- 
ence to,  38. 

Typical  voltaic  cell,  description  of,  3. 

U  OR  HORSESHOE  MAGNET,  26. 

Unit  of  magnetism,  83;  of  magnetic  induc- 
tion, Kapp's,  83  ;  English,  83 

Units,  lundamental  and  derived,  37 ;  elec- 
trical, synoptical  table  of,  73  ;  practical, 
derived  from  natural  constants,  59. 

Universal  switchboard,  156 ;  manipulation  of, 
157' 

U.  S.  Coast  and  Geodetic  Survey,  reference  to 
reports  of,  40. 

VAIL,  ALFRED,  biographical  notice  of,  216 ; 
originator  of  the  telegraphic  register  in  its 
present  form,  216 ;  of  the  alphabetical 
code,  216. 

Varley's  insulator,  tests  of  efficiency  of,  120  ; 
loop  test  for  position  ot  escape  on  line, 
203. 

Varley's  Report  on  Western  Union  Lines, 
references  to,  131,  135. 

V-gauge  for  wire,  95. 

Victor  Key,  140. 

Volt,  the  unit  of  electromotive  force,  defini- 
tion of,  61  ;  value  of,  61. 

Volta,  Alessandro,  biographical  notice  of, 
61. 

Volta  induction,  74. 

Voltaic  cell,  phenomena  of,  5;  directions  for 
charging,  7. 

Voltaic  effect,  chemistry  of,  6. 

Voltaic  element,  the,  3. 

Voltaic  solutions.  Becker's  table  of  resist- 
ances of,  63  ;  Farmer's  ditto,  62. 

Voltameter,  the,  44. 

Voltmeter,  use  of  in  telegraphic  testing.  210 ; 
Weston's  portable,  210-  advantages  of 
for  testing,  211  :  Weston's  combined  am- 
meter and,  for  telegraphic  testing,  210,  211. 


234 


Index. 


WASHBURN  &  MOEN   MVc  Co.'s  IRON  WIRE 

TABLE,  112. 

Watt,  James,  biographical  notice  of,  73. 
Watt,  the  unit  of  power  or  rate  of  work, 
value  of,  73  ;   rule  for  determination  of, 

Way-station,  arrangement  of  apparatus  at, 
151  ;  connections  ot,  152  ;  manipulation  of 
switchboard  in,  153  ;  testing  in,  154. 

Weather- cross,  term  applied  to  escape  be- 
tween different  wires,  132. 

Webb,  F.  C.,  on  electrostatic  phenomena, 
175. 

Webb's  Electrical  Accumulation  and  Con- 
duction, extract  from,  175. 

Weber,  Eduard,  83. 

Wedge  or  plug  cut-out,  the,  155. 

Weights  of  iron  and  copper  wires  for  tele- 
graph lines,  table  of,  112. 

Western  Electric  key,  140. 

Western  Union  glass  insulators,  116. 

Western  Union  Telegraph  Company's  forms 
for  test  sheets,  212,  213,  214. 

Western  Union  telegraph  station,  New  York, 
arrangement  ot  dynamos  in,  170. 

Weston's  voltmeters  and  ammeters  for  tele- 
graphic testing,  210,  211. 

Wheatstone  bridge,  the,  195. 

Wilkinson,  Kennelly  and,  85. 

Winding  magnet  helices,  machine  for,  93. 

Windings  ot  helix,  effect  of  position  of,  92. 

Windings  of  magnet  coils,  Sir  Wm.  Thom- 
son's rule  for  computing,  94. 


Wire-gauge,  American  standard,  95  ;  British, 

95. 
Wire,   instruments  for  gauging,  95,  96 ;   in 

helix,  relation  of  length  and  thickness  ot 

to  number  of  turns,  92. 
Wires,  copper,  for  line  construction,  114;  lor 

magnets,  dimensions  and  resistances  of, 

93  ;  Prescott's  table  of,  94. 
Wires,  crossing  01,  represented  in  diagram, 

104. 
Wires,  iron,  in  ;  table  of  sizes,  weights,  and 

resistances  of,   112;   joints  in,  113;    dia- 
gram of  actual  sizes  of,  113. 
Wood's  repeater,  164. 
Word-space,  an  element  of  telegraphic  code, 

216. 

Work,  electric,  in  circuit,  64. 
Working  efficiency  of  telegraph  line,  what  it 

depends  on,  127. 

YOKE,  of  electro-magnet,  91. 

Youmans'  Correlation  and  Conservation  y 
Forces,  reference  to,  38. 

ZINC  OF  GRAVITY  CELL,  4;  process  ot  clean- 
ing, 16;  amalgamation  of,  21. 

Zinc,  oxide  of,  formed  by  action  of  voltaic 
cell,  6. 

Zinc,  electro-chemical  equivalent  of,  74,  75; 
chemical  analysis  of,  9. 

Zinc  solution  of  gravity  cell,  neutralizatioB 
of,  1 6. 

Zinc  plate  of  cell  the  positive  element,  12. 

Zinc,  d'Infrcvillc's  wasteless,  33. 


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fully revised  by  W.  H.  Preece.  12mo,  cloth.  Illustrated.  $4.00. 

NOLL,  AUGUSTUS.  How  to  Wire  Buildings.  A  Manual  of  the  Art  of  Interior 
Wiring.  Fourth  Edition.  8vo,  cloth.  Illustrated.  $1.50. 

OHM,  Dr.  G.  S.  The  Galvanic  Circuit  Investigated  Mathematically.  Berlin, 
1827.  Translated  by  William  Francis.  With  Preface  and  Notes  by  the 
Editor,  Thos.  D.  Lockwood.  12mo,  cloth.  (No.  102  Van  Nostrand's 
Science  Series.)  50  cents. 

PALAZ,  A.  Treatise  on  Industrial  Photometry.  Specially  applied  to  Electric 
Lighting.  Translated  from  the  French  by  G.  W.  Patterson,  Jr.,  Assistant 
Professor  of  Physics  in  the  University  of  Michigan,  and  M.  R.  Patterson,  B.A. 
Second  Edition.  Fully  Illustrated.  Svo,  cloth.  $4.00. 

PARSHALL,  H.  F.,  and  HOBART,  H.  M.  Armature  Windings  of  Electric 
Machines.  With  140  full-page  plates,  05  tables  and  descriptive  letter-press. 
4to,  cloth.  $7.50. 

PERRY,  NELSON  W.  Electric  Railway  Motors.  Their  Construction,  Operation, 
and  Maintenance.  An  Elementary  Practical  Handbook  for  those  engaged  in 
the  management  and  operation  of  Electric  Railway  Apparatus,  with  Rules 
and  Instructions  for  Motormen.  12mo,  cloth.  $1.00. 

PLANTE,  GASTON.  The  Storage  of  Electrical  Energy,  and  Researches  in  the 
Effects  created  by  Currents  combining  Quantity  with  High  Tension.  Trans- 
lated from  the  French  by  Paul  B.  Elwell.  89  Illustrations.  Svo.  $4.00. 

POOLE,  J.  The  Practical  Telephone  Handbook,  and  Guide  to  the  Telephonic 
Exchange.  Second  Edition.  Revised  and  enlarged.  Illustrated.  Svo, 
cloth.  $1.50. 

POPE,   F.   L.     Modern  Practice  of  the  Electric   Telegraph.     A   Handbook    for 
'     Electricians   and  Operators.     An   entirely  new   work,  revised   and   enlarged, 
and  brought  up  to  date  throughout.     Illustrations.     Svo,  cloth.     31.50. 


O.V  ELECTRICAL   SCIENCE  449 

PREECE,  W.  H.,  and  STUBBS,  A.  J.  Manual  of  Telephony.  Illustrated.  12mo, 
cloth.  $4.50. 

RECKENZAUN,  A.     Electric  Traction.     Illustrated.     Svo,  cloth.     §4.00. 

RUSSELL,  STUART  A.  Electric-Light  Cables  and  the  Distribution  of  Elec- 
tricity. 107  Illustrations.  8vo,  cloth.  $2.25. 

SALOMONS,  Sir  DAVID,  M.A.  Electric-Light  Installations.  A  Practical  Hand- 
book. Seventh  Edition,  revised  and  enlarged.  Vol.  I. :  Management  of 
Accumulators.  Illustrated.  12mo,  cloth.  $1.50.  Vol.  II.:  Apparatus. 
Illustrated.  12mo,  cloth.  $2.25.  Vol.  III.:  Application.  Illustrated. 
12mo,  cloth.  $1.50. 

SCHELLEN,  Dr.  H.  Magneto-Electric  and  Dynamo-Electric  Machines.  Their 
Construction  and  Practical  Application  to  Electric  Lighting  and  the  Trans- 
mission of  Power.  Translated  from  the  third  German  edition  by  N.  S. 
Keith  and  Percy  Neymann,  Ph.D.  With  very  large  Additions  and  Notes 
relating  to  American  Machines,  by  N.  S.  Keith.  Vol.  I.  with  353  Illus- 
trations. Third  Edition.  $5.00. 

SLOANE,  Prof.  T.  O'CONOR.  Standard  Electrical  Dictionary.  300  Illustra- 
tions. 8vo,  cloth.  $2.50. 

SNELL,  ALBION  T.  Electric  Motive  Power.  The  Transmission  and  Distribution 
of  Electric  Power  by  Continuous  and  Alternate  Currents.  With  a  Section 
on  the  Applications  of  Electricity  to  Mining  Work.  Illustrated.  Svo, 
cloth.  $4.00. 

SWINBURNE,  JAS.,  and  WORDINGHAM,  C.  H.  The  Measurement  of  Elec- 
tric Currents.  Electrical  Measuring  Instruments.  Meters  for  Electrical 
Energy.  Edited,  with  Preface,  by  T.  Commerford  Martin.  Folding  Plate 
and  numerous  Illustrations.  16mo,  cloth.  50  cents. 

THOM,  C.,  and  JONES,  W.  H.  Telegraphic  Connections,  embracing  recent  meth- 
ods in  Quadruplex  Telegraphy.  Twenty  colored  plates.  Svo,  cloth.  $1.50. 

THOMPSON,  EDWARD  P.  How  to  Make  Inventions;  or,  Inventing  as  a 
Science  and  an  Art.  An  Inventor's  Guide.  Second  Edition.  Revised 
and  Enlarged.  Illustrated.  Svo,  paper.  $1.00. 

THOMPSON,  'Prof.  S.  P.  Dynamo-Electric  Machinery.  With  an  Introduction 
and  Notes  by  Frank  L.  Pope  and  II.  R.  Butler.  Fully  Illustrated.  (No.  66 
Van  Nostrand's  Science  Series.)  50  cents. 

Recent  Progress  in  Dynamo-Electric  Machines.  Being  a  Supplement  to 
"Dynamo-Electric  Machinery."  Illustrated.  12mo,  cloth.  (No.  75  Van 
Nostrand's  Science  Series.)  50  cents. 

The  Electro-Magnet  and  Electro-Magnetic  Mechanism.  Second  Edition, 
revised.  213  Illustrations.  Svo,  cloth.  $6.00. 

TREVERT,  E.     Practical  Directions  for  Armature  and  Field-Magnet  Winding. 

Illustrated.      12mo,  cloth.     $1.50. 

How  to  Build  Dynamo-Electric  Machinery.  Embracing  the  Theory,  Designing, 
and  Construction  of  Dynamos  and  Motors.  With  Appendices  on  Field- 
Magnet  and  Armature  Winding,  Management  of  Dynamos  and  Motors,  and 
useful  Tables  of  Wire  Gauges.  Illustrated.  Svo,  cloth.  $2.50. 

TUMLIRZ,  Dr.  Potential,  and  its  Application  to  the  Explanation  of  Electri- 
cal Phenomena.  Translated  by  D.  Robertson,  M.D.  12mo,  cloth.  -$1.25. 


450  LIST  OF   IVOKKS   O.Y  ELECTRICAL   SCIENCE. 

TUNZELMANN,  G.  W.  de.  Electricity  in  Modern  Life.  Illustrated.  12mo, 
cloth.  $1.25. 

URQUHART,  J.  W.  Dynamo  Construction.  A  Practical  Handbook  for  the  Use 
of  Engineer  Constructors  and  Electricians  in  Charge.  Illustrated.  12mo, 
cloth.  §3.00. 

Electric  Ship-Lighting.  A  Hand-book  on  the  Practical  Fitting  and  Running  of 
Ships'  Electrical  Plant,  for  the  Use  of  Ship  Owners  and  Builders,  Marine  Elec- 
tricians and  Sea-going  Engineers  in  Charge.  88  Illustrations.  12mo,  cloth. 
$3.00. 

Electric  Light  Fitting.  A  Hand-book  for  Working  Electrical  Engineers,  Em- 
bodying Practical  Notes  on  Installation  Management.  Second  Edition,  with 
additional  chapters.  With  numerous  Illustrations.  12mo,  cloth.  $2.00. 

WALKER,  FREDERICK.  Practical  Dynamo-Building  for  Amateurs.  How  to 
Wind  for  any  Output.  Illustrated.  16mo,  cloth.  (No.  98  Van  Nostrand's 
Science  Series.)  50  cents. 

WALMSLEY,  R.  M.  The  Electric  Current.  How  Produced  and  How  Used. 
With  379  Illustrations.  12mo,  cloth.  $3.00. 

WEBB,  H.  L.  A  Practical  Guide  to  the  Testing  of  Insulated  Wires  and 
Cables.  Illustrated.  12mo,  cloth.  $1.00. 

WORMELL,  R.  Electricity  in  the  Service  of  Man.  A  Popular  and  Practical 
Treatise  on  the  Application  of  Electricity  in  Modern  Life.  From  the  Ger- 
man, and  edited,  with  copious  additions,  by  R.  Wormell,  and  an  Introduc- 
tion by  Prof.  J.  Perry.  WTith  nearly  850  Illustrations.  Royal  8vo,  cloth. 
$5.00. 

WEYMOUTH,  F.  MARTEN.  Drum  Armatures  and  Commutators.  (Theory  and 
Practice.)  A  complete  treatise  on  the  theory  and  construction  of  drum- 
winding,  and  of  commutators  for  closed-coil  armatures,  together  with  a  full 
resumt  of  some  of  the  principal  points  involved  in  their  design  ;  and  an 
exposition  of  armature  reactions  and  sparking.  Illustrated.  8vo,  cloth. 
$3.00. 


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